Volunteers Dig In and Dig Out at Hyatt Reserve

More than 90 volunteers made quick work of planting 550 shrubs at the City of Boise’s Hyatt Hidden Lakes Reserve on April 14 as part of the Boise River Enhancement Network’s cooperative project to improve wildlife habitat and decrease fire risk.  Re-establishing native plants and controlling weeds is recommended in the Boise River Enhancement Plan. The volunteers included members of Rotary Clubs from across the Treasure Valley and 32 youth from Boy Scout Troop 100 and the Idaho Fine Arts Academy Interact Club.


Martha Brabec, Boise Parks and Recreation Restoration Specialist said, “This site used to be a gravel pit, and most of the native vegetation was removed. We’re rebuilding the natural habitat and creating important diversity for the birds that live here and stop over during migration. Thousands of new plants will be in the ground by the time the project is complete.”


The project aligned perfectly with Rotary International’s 1.2 Million Tree Planting Challenge; a national campaign to plant one tree for each member of Rotary. It also was a great fit for Jayanth Mouli, a sophomore at Boise High School who selected this conservation project for his Eagle Scout service project.

Earlier in the day, hundreds of native plants destined for planting at the reserve were transplanted to “conetainers” for the summer. Members of the Silver Sage Girl Scout Council, Big Brothers Big Sisters of Southwest Idaho and others had gathered and planted the seeds in the fall. The seedlings needed bigger quarters, and the volunteers carefully separated the sprouts and replanted them in cone-shaped containers that provide plenty of space. Sean Finn of the Golden Eagle Audubon Society said, “Growing plants is an exciting way for kids to be part of the Hyatt project. It’s a win-win because plants grown from local seeds have a better chance to survive.” 


The new plants are already changing the look of the hillsides at the reserve, but it’s critical to keep down the weeds that can out-compete the native plants. On April 25, 25 volunteer Weed Warriors took to the reserve with trowels and shovels eagerly digging out thistle, teasel and other weeds. Martha Brabec identified the weeds and demonstrated the best method to use. Many of the volunteers visit the reserve regularly, and they promised to continue the weeding on their own now that they have guidance.


Nestled in a residential and commercial area in West Boise, the ponds, wetlands and hillsides of the reserve blend together to create a unique pocket of wildlife habitat in the center of urban Treasure Valley. The reserve enjoys year-round use by people attracted by the rich bird life, the wide paths and the outstanding scenery. The 18-month multicultural habitat enhancement project is led by the Land Trust of the Treasure Valley, Boise River Enhancement Network and City of Boise Department of Parks and Recreation.

Project partners include U.S Fish and Wildlife Service, Idaho Office of Refugees by Jannus, Big Brothers Big Sisters of Southwest Idaho, Golden Eagle Audubon Society, Intermountain Bird Observatory, Boise State University, College of Western Idaho, The Wetlands Group, Idaho Weed Awareness Campaign, Rotary International and Partners for Clean Water.

Cooperative Project Will Remove Tons of Sediment

Work Begins on Water Quality Protection Project

The Farmers’ Co-operative Ditch Company of Parma is breaking new ground in northwest Canyon County as work gets underway on an 8.8-acre sediment basin designed to remove 2,000 tons of sediment from the water in the canal. When completed, canal water will be diverted into the sediment basin and travel a sinuous 2,000 ft before returning to the canal for delivery to producers. Many Farmers’ Co-op shareholders currently receive water with large amounts of sediment that damages pumps, clogs irrigation systems and accumulates in concrete ditches.

Farmers’ Co-operative Ditch Company Directors

After irrigating crops, the water drains to either the Boise River or the Snake River depending on the location of the farm.  Water quality in both rivers is impaired by excess sediment and nutrients. Federal plans are in place to bring the rivers into compliance with water quality standards that protect the aquatic ecosystem and recreational river users. Agricultural compliance with the plans is voluntary, and public/private cost-sharing projects like this one are critical to implement needed improvements.








Farmer’s Co-operative Ditch near Parma                                Site of the sediment basin

The project is the first sediment basin developed and managed by an irrigation delivery entity in the Lower Boise River watershed. The Farmer’s Co-op is leasing the land for the sediment basin and providing staff and shareholder support. $500,000 from the USDA-Natural Resources Conservation Service Regional Conservation Partnership Program will help build the sediment basin and also provide matching funds for Farmers’ Co-op shareholders that install on-farm conservation practices to reduce water usage and improve soil health. Project Fact Sheet.

This ambitious project aligns perfectly with recommendations in the Boise River Enhancement Network’s  Boise River Enhancement Plan.  On-site enhancement, like the on-farm best management practices that will be implemented through the project, is recognized as the best way to improve water quality. Conversion to sprinkler or drip irrigation and precise application of fertilizer are two BMPs that improve water quality. Construction of sediment basins is also recommended as an effective way to reduce sediment and nutrients entering the river.

Project partners include the USDA-NRCS, Lower Boise Watershed Council, and Canyon Soil Conservation District.

Photos by Bob Braun and Lori Kent

     Dan Steenson     large group    Tom Johnston

Directors of the Farmers’ Co-operative Ditch Company, Canyon Soil Conservation District, and Lower Boise Watershed Council celebrate the groundbreaking on April 6, 2018 along with staff of NRCS.

More Than Waterfowl at Hyatt Hidden Lakes Reserve

By Heidi Ware, Education and Outreach Director for the Intermountain Bird Observatory

Hyatt Hidden Lakes Reserve teems with birds. Birders come to Hyatt in droves for the excellent views of charismatic species like Ruddy Ducks, with their bright blue bills. Or the families of Pied-billed Grebes with their odd, croaking calls and cute zebra-striped babies. Birders and passers-by marvel at the Great Blue Herons, Belted Kingfishers, and Ospreys fishing–each in their own way. We think of the raucous calls of Yellow-headed Blackbirds, the classic Red-winged Blackbird “conk-a-ree”, and the raspy, energetic chatter of Marsh Wrens.

When the reserve was formed, a restoration effort created excellent wetland habitat that attracts a great variety of species.


Photo Kathy Hopkins



A male Northern Shoveler swims on the pond at Hyatt wetland. Northern Shovelers are common visitors to Hyatt during the Fall, Winter, and Spring.


Photo Kathy Hopkins


A Yellow-headed Blackbird sits in the sun atop cattails at Hyatt Hidden Lakes Reserve.

Photo Kathy Hopkins







Hyatt Hidden Lakes Reserve is Home to More than Waterfowl!

If you look at the species list, Hyatt may host a huge variety of waterbirds, but in reality, more than half the species that call Hyatt home also rely on its upland habitat for survival! American Kestrels hunt for mice and grasshoppers in the shrubs and fields. California Quail, Black-billed Magpies, and numerous Sparrow species rely on Sagebrush and other shrubs for food, shelter, and warmth.

An American Kestrel snacks on a Grasshopper at Hyatt Hidden Lakes.  A Black-billed Magpie at Hyatt Hidden Lakes. Photos by Ken Miracle


The cover that Hyatt’s upland habitat provides means birds have a home year-round, even during the cold of winter, when shelter is especially important. And while birds already love and use Hyatt Hidden Lakes Reserve, the upland habitat is not what it could be.

a male and female California Quail snuggle together in the sunshine on a snowy day

Two California Qual snuggle in the warm shelter of Hyatt’s upland habitat. Photo by Idaho Birding admin Tom Carroll

A number of invasive grasses and shrubs have taken over large patches of Hyatt, making it less attractive to birds than the native plants that should be there. If you can believe it, Hyatt could someday be even more valuable habitat for birds with just a little TLC.

Upland habitat restoration is underway!

I hope you’ll join me, and the rest of the birdwatching and nature loving community, in supporting the Hyatt Hidden Lakes Habitat Enhancement Project. There’s a lot of work to do and a lot of room for enthusiastic volunteers to pitch in. As a fan of Hyatt, I cannot wait to watch the bird list grow even larger as the habitat continues to improve.

To hear what we’re doing to make Hyatt even better, don’t forget to attend our BREN Brown Bag Lunch Program on April 11 at the Boise Library at 11:30 am.

To learn more about the birds that call Hyatt home, be sure to join the Idaho Birding Facebook community. Our local Golden Eagle Audubon Society often visits Hyatt during their group field trips.

You can also view a species list and illustrated checklist of Hyatt’s bird diversity on eBird. Or, even add your own observations of Hyatt’s bird life by submitting your own eBird checklist.


ACHD Invests to Protect the River

Unbeknownst to most harried commuters, Ada County Highway District (ACHD) is reducing pollution of the Boise River as part of many road improvement projects. ACHD is leading the valley in investment in roadway Green Stormwater Infrastructure (GSI), and new projects on State St. and Franklin Road demonstrate two different techniques. While ACHD has not permitted new discharges of stormwater to the Boise River for decades, stormwater from hundreds of miles of older roads travels through pipes to the Boise River carrying sediment, bacteria, nutrients, oil, grease, and heavy metals. Gross!

The Blooming of 15th and State St.

Bioretention planters were placed along the northwest, southeast, and southwest areas of the intersection of 15th and State St. in downtown Boise.  The planters will be backfilled with bioretention soil media (BSM), a nutrient-rich, permeable, engineered soil matrix comprised of sand, aged compost, and trace silt.  Plants selected for their ability to flourish in this unusual environment, including Joe Pye weed, Purple Maiden Grass, Culver’s root, ‘Black Adder’ Anise Hyssop, and Orange Coneflower, will be planted.

In a large storm event, approximately 6,100 gallons of stormwater will enter the planters instead of discharging to the Boise River untreated.  Additionally, the planters will beautify the intersection and offer habitat for invertebrates including important pollinators like native bees and butterflies. Bioretention planters can also be found on Royal Blvd.

  Orange Coneflower       Idaho fescue

Bioretention Swales Spruce Up Franklin Rd.

A different technique well suited for long stretches of rural roads is now in place on approximately .75 mile of Franklin Road between Black Cat Rd. and Ten Mile Rd. Bioretention swales were installed along both sides of Franklin Road and all four legs of the Franklin/Black Cat intersection.  The bioretention swales are filled with BSM and were seeded in December 2017 with a native seed mix that includes drought tolerant grasses and wildflowers including western yarrow, California poppy, Blanketflower, Lewis flax, Scarlet globemallow, Sideoats grama, Thickspike wheatgrass, Idaho fescue, Sheep fescue, and Sandberg bluegrass. 

Bioretention swale on the north side of Franklin Rd. under construction.

The swales are sized to retain approximately 253,437 gallons of runoff in a large storm event.  Prior to installation of the swales, no stormwater system was in place along these sections of Franklin Rd. and Black Cat Rd., and runoff flowed overland into Purdam Gulch Drain or Kennedy Lateral then to Tenmile Creek and on to the Boise River.  Like the planters on State St., the Franklin Rd. project swales will help to retain and remove pollutants from runoff before it enters our surface water.

ACHD is an independent government entity that controls 2,100 miles of roads in Ada County. ACHD Commissioners are elected by region .


Yellow Warblers Flock to the Boise River

Used by permission of the Intermountain Bird Observatory

For the past few months, Sage International School senior, Zoe Daly has been working on a project using Yellow Warbler data from the Intermountain Bird Observatory’s Boise River Research Station.

A Yellow Warbler is weighed at our Boise River Site, just before being released. Photo by Tom Carroll

A Yellow Warbler is weighed at our Boise River Site, just before being released. Photo by Tom Carroll

In the Fall of 2017 IBO ran nets daily during fall migration for the first time ever! This gave us an excellent, fine-scale picture of migration at the river station. We were also able to complete a full MAPS breeding season banding protocol this summer, sampling songbirds at the site once every 10 days. Simultaneously, we collected the same data at our long-standing Lucky Peak station.

This gave us the ability to compare between our Boise River and Lucky Peak stations like never before.

When we first started banding at the Boise River site, we knew that it was special for Yellow Warblers (we once caught more than 200 of them in a single day!) but we had never looked at the hard data or quantified exactly what was going on. So, when Zoe came along and told us she loved looking at data and graphs, we knew exactly what she should do.

The Cottonwood overstory and thick willow, currant, and rose shrub layer at our Boise River Site is ideal habitat for Yellow Warblers.

The cottonwood overstory and thick willow, currant, and rose shrub layer at our Boise River Site is ideal habitat for Yellow Warblers. Photo by Tom Carroll

Zoe took our banding data from Lucky Peak and the Boise River and compared Yellow Warblers at both sites. In particular, she looked at the fat levels of Yellow Warblers.

She found that Yellow Warblers were significantly fatter at our Boise River Station than at Lucky Peak.

This means that the habitat at the Boise River provides food that Yellow Warblers need during migration and stopover. They are able to spend time at the site, eat, and “fuel up” with fat for the next leg of their migration journey.

Zoe also found that Yellow Warblers at Lucky Peak tend to leave the area soon after their young fledge…they don’t stay at the site during late summer when migrants begin fattening up. Instead, they seem to travel to the river to finish molting and fattening up for migration.

This goes to show that the riparian habitat at the Boise River is a key resource for neotropical migrants like Yellow Warblers.

Congratulations to Zoe for completing this poster and finding such interesting results! Thanks also to Guy Falconer of Sage International School who connected Zoe with IBO to begin this internship.

Check out Zoe’s full poster to learn more:Poster showing graphs of Yellow Warbler fat levels. Yellow Warblers were fatter at the Boise River than at Lucky Peak

(full size poster PDF available here)

Why Do Beavers Eat Willows?

Have you ever heard of a beaver with a headache? Probably not. Beavers eat willow plants that contain the active ingredient in aspirin. And they don’t have to worry about child-proof caps.

You can learn about the medicinal and traditional uses of many plants that grow at the City of Boise’s Hyatt Hidden Lakes Reserve at the Hyatt Multi-Cultural Habitat Enhancement Project Open House on March 7 from 5:30-7:30 at the Boise Watershed, 11818 W Joplin, Boise 83714.

Roger Rosentreter Photo courtesy of Riverside Hotel

Plant ecologist, teacher and author Roger Rosentreter Ph. D will share his ethnobotanical knowledge of Idaho’s native plants. Martha Brabec, City of Boise Open Space Restoration Specialist will talk about invasive plants at the reserve and the ongoing control strategies.  BREN volunteer Conner Jackson will explain why Russian olive trees are being removed. Eric Willadsen of the Land Trust of the Treasure Valley will provide an update on the Hyatt Multi-Cultural Habitat Enhancement Project including upcoming opportunities to be part of this cooperative effort. The presentations start at 6:00 pm.

Before and after the presentations, you can visit with representatives from the Idaho Weed Awareness Campaign, Deer Flat National Wildlife Refuge, Idaho Firewise, Community Native Plant Nursery, Boise River Enhancement Network and more. The educational exhibits at the Boise WaterShed will be open for the kids to enjoy during the open house.

Community Members Grow Native Plants for the Reserve

With spring right around the corner, Hyatt Multi-Cultural Habitat Enhancement Project partners are preparing to transplant native plant seedlings from germination trays into cones for the summer growing season. Over the past three months, volunteers planted more than 50 germination trays with seeds gathered from the reserve and other Treasure Valley locations. Members of Girl Scout Troop 105 pictured below are growing two trays from seeds they planted in January. Those plants will find a new home in the reserve next fall.


Weeds Warriors Comes to Hyatt Reserve

The battle to control weeds at the reserve begins anew in the spring, and this year Weed Warriors will be trained to tackle the task. Weed Warriors are specially-trained volunteers who adopt specific areas to pull weeds on a regular basis.  According to Martha Brabec, Weed Warriors made a difference in the foothills in 2017, and she’s excited to provide a training specifically for the Hyatt Hidden Lakes Reserve on April 25. Field trips to the reserve for new residents from many nations and others will also be on the project schedule for the spring when migrating birds are at the reserve.

Improving Habitat and Enriching Lives Together

Seedling planted by volunteers at Hyatt Reserve. Photo by Art Robertson.

The Hyatt Multi-Cultural Habitat Enhancement Project is led by the Land Trust of the Treasure ValleyBoise River Enhancement Network, and the City of Boise. Project partners include U.S Fish and Wildlife Service, Idaho Office of Refugees by Jannus, Big Brothers Big Sisters of Southwest Idaho, Golden Eagle Audubon Society, Intermountain Bird Observatory, Boise State University, The Wetlands Group, Idaho Fish and Game, Idaho Weed Awareness Campaign, and Partners for Clean Water. The goals of the project are to establish bird-friendly, fire-resistant vegetation on hillsides at the reserve and help community members of all backgrounds connect to this unique outdoor space.

Russian Olive Trees at Hyatt Hidden Lakes Reserve

By Conner Jackson

A walk through the city of Boise’s Hyatt Hidden Lakes Reserve in the middle of the winter is a great time to see plants in their dormant phase. Especially easy to pick out in the winter at Hyatt is the Russian olive– a non-native small tree or shrub that grows in abundance on the shores of each of the lakes.  If you’re a frequent visitor to the reserve, you’ll easily note the spread of Russian olives over the past decade.The City’s embarking on an ambitious plan to reduce the Russian olive population at the reserve, a plan that will improve bird habitat at the reserve.

Russian olive trees at Hyatt Reserve. Photo by Conner Jackson.

Russian olive, Elaeagnus angustifolia., is a deciduous shrub or small tree native to southern Europe and Asia. It has thin, silvery-gray leaves and reddish bark that is commonly covered in sharp thorns. They can grow up to 45 feet tall.

Russian olive trees have nasty thorns. Photo by Conner Jackson.




Right now, the leaves of Russian olives have fallen, but in the springtime, the trees will leaf out and produce yellow flowers and small, oval shaped fruits. Those fruits will likely be eaten birds and other animals in the reserve when they are fully ripened in the fall.

Russian olive trees are very capable plants that have spread widely since their introduction. They can tolerate infrequent fire, browsing, temporary flooding, and mechanical cutting.  Russian olive can grow from seeds dispersed by wildlife, stump sprouts, stem cuttings, and root pieces. They were planted across North America since the early 1900s for windbreaks, erosion control, and to provide food and cover for wildlife. Russian olive trees are found extensively in wet-saline and riparian environments, including Hyatt Hidden Lakes Reserve.

The problem is the Russian olive is too capable. The trees are quick to displace native species such as willows and cottonwoods by outcompeting them for resources, including access to sunlight and water.  The Russian olive is a poor replacement for the native plants. Aside from their fruit Russian olive trees are not edible by birds and wildlife found in in the Boise River watershed.  They can crowd out other plant species that provide great habitat for wildlife.

Herbicide applied to the stumps prevents regrowth.

Volunteers removed Russian olive trees in November 2017.








The City of Boise, as part of a reserve habitat improvement project, is removing Russian olive trees. Both City Forestry crews and volunteers, including BREN members, are involved. The goal is to prevent Russian olive trees from completely crowding out desired native species. Trees of all sizes are being removed and stumps are being treated with herbicide so they don’t re-sprout. Vegetation is so dense around the lakes, that open spaces created by Russian olive removal are expected to be quickly filled by native plants. Not every Russian olive tree will be removed to preserve aesthetics and the buffer between Maple Grove Rd. and the reserve.

Learn more about BREN’s cooperative Hyatt Hidden Lakes Reserve Habitat Enhancement Project. Join BREN, the Land Trust of the Treasure Valley and City of Boise for a Hyatt Reserve Open House where you’ll hear from Conner and others.

The Power of Cover Crops

By Jessica Harrold, Ada Soil &  Water Conservation District

Agriculture is big business in the Treasure Valley. Area farmers produce a wide variety of crops including hops, award-winning wines, onions, mint and the great Idaho sugar beet. While the sunny climate and availability of irrigation water contributes to the bountiful harvest, the quality of the soil is paramount. Protection and improvement of the soil has captured the attention of organizations around the Treasure Valley, and they’re working with area farmers to study soil health and implement best management practices.

Side by Side Fields Were Studied

One study focused on the use of cover crops. Cover crops can prevent erosion and increase organic matter in the soil, improving water infiltration rates and sequestering carbon. Using Conservation Innovation Grant funding from the Natural Resources Conservation Service, the Ada Soil & Water Conservation District (Ada SWCD) followed three local producers as they integrated new planting methods and cover crops into their farm management plans. The study monitored erosion rates, soil health, and costs/profits.

Conventionally tilled and planted fields were compared to fields where seeds were planted with a no-till drill that eliminates soil disturbance. The no-till fields showed reduced rates of erosion and reduced phosphorus output, having a direct benefit on water quality in the Snake River. The no-till fields also had a higher water infiltration rate with a corresponding reduction in dry areas.

Each no-tilled field also showed improved soil health; the percent of organic material increased. The no-till plots required less tractor work that saved fuel and time. The producers were also able to use less fertilizer. This all added up to cost savings. In the case of grazing, using cover crops in place of winter feed saved farmers hay costs and time while improving their soil for the next year’s crop. Two short videos about the study can be viewed here.

Local Soil Health Projects

The Ada SWCD has also implemented a grant program to support local soil protection and improvement projects. Two grants have recently been awarded. The Treasure Valley Food Coalition soil education project is teaming with universities to offer programs to students and the public. The spring programs focus on soil structure and the reliance we have on healthy soil. Fall programs will focus on the mycorrhizae in the soil and how to help them flourish.

Horses for Clean Water is partnering with the Idaho Equine Hospital to offer courses that focus on animal and pasture health. They focus on proper land management, including mud and manure management, proper grazing, and land stewardship to protect the natural resources around your property.

Read more about soil health in this BREN blog by Erin Brooks, Natural Resources Conservation Service.

Upcoming Soil Education Events
February 7 | A Holistic Approach to Manure Management
6:30-8:30 pm, Idaho Equine Hospital, 16080 Equine Drive, Nampa

February 15 | Soil Health Symposium
7:30-4:30, Four Rivers Cultural Center

March 7 | Pasture Management and Equine Health and Nutrition
6:30-8:30 pm, Idaho Equine Hospital, 16080 Equine Drive, Nampa

March 10 | Garden Soil Testing Workshops
North End Organic Nursery, Edwards Greenhouse, Franz Witte

April 2 | Lecture: Dr. David Montgomery
6:30 pm, Jordan Ballroom, Boise State University Student Union Building

April 21 | Soil Dig with University of Idaho
10:00 am, Fiddlers Green Farm

The Importance of Soil Health

By Erin Brooks, Natural Resources Conservation Service

It would have been hard to find any reference to soil health twenty years ago. Soil was conventionally treated as an inert growing medium. Today’s explosion of interest in soil health reflects a fundamental shift in soil science and a corresponding shift in the way we care for our nation’s soils. Soil is now recognized as a living ecosystem teeming with billions of bacteria, fungi, and other microbes that are the foundation of an elegant symbiotic ecosystem.

The complex soil ecosystem provides numerous benefits. These include:
1. Creating nutrients for plant growth,
2. Absorbing and holding rain for plant use during dry periods, and
3. Preventing soil and pollutants from leaving farm fields.

Healthy soil serves as a firm foundation for agricultural activities

Soil health is dynamic and changes in response to management practices.  Management practices can affect the amount of organic matter in the soil, the presence of which is critical for soil ecosystem function. Management practices also affect soil structure, soil depth, and water and nutrient holding capacity.  Soil health is improved when farmers mimic nature; when the myriad of creatures that comprise the soil food web are cared for and not abused.  A fully functioning soil produces the maximum benefit at the least cost.

It is crucial to integrate and follow all soil health management principles for the soil to become and remain healthy.

5 Principles of Soil Health

  1. 1. Minimizing soil disturbance
    2. Maximizing diversity of plants/crops
    3. Keep living roots in the soil
    4. Keep the soil covered with plants or residue at all times
    5. Incorporate livestock

The Boise River Enhancement Plan recommends adoption of these agricultural best management practices to enhance water quality in the Boise River and its tributaries.

Residue left between crop rows – no bare ground

Cover Crop – maximizing a living root, ground cover and plant diversity

Bringing Our Soil Back to Life

You can learn more about soil health and agricultural best management practices at the 9th Annual Soil Health Symposium on February 15.  Speakers include David Montgomery – University of Washington, Olga Walsh – University of Idaho, Shawn Nield – Idaho NRCS and Joel Packman – University of Idaho. The symposium will be held at the Four Rivers Cultural Center in Ontario, OR. Information and registration

Unique Partnership Will Reduce Boise River Pollution

by Dr. Jack Harrison

Water in the Boise River will have less sediment and phosphorus because of a new partnership between the City of Middleton and Drainage District No. 2 (DD2). The innovative water quality improvement project will remove sediment and phosphorus from the Mill Slough, a major Boise River tributary. This partnership between the City and DD2 demonstrates how cities and the agricultural community can work together to reduce non-point pollution in the Boise River watershed.

Mayor Taylor

Middleton Mayor Darin Taylor leads a tour at the Mill Slough project site

on tour

Chris Yarbrough, IDFG and Jessica Harrold, Ada Soil and Water Conservation District and BREN visit the project site.








Middleton Mayor Darin Taylor said, “The Boise River is our front yard and we want to take care of it. We created this opportunity to partner with Drainage District 2 and do something neither of us could do on our own.”

Irrigation return often carries sediment and phosphorus

The Mill Slough discharges to the Boise River near Middleton Road and is one of twelve Boise River tributaries identified in the 2015 Lower Boise River Total Maximum Daily Load (TMDL) that need to contribute less sediment, bacteria and nutrients to the Boise River. According to US Geological Survey data, Mill Slough has the fifth highest discharge of total phosphorus when compared to other Boise River tributaries. Discharge loads average 125 pounds per day.


Project engineer Jack Harrison, HyQual

The Mill Slough is an integral part of DD2’s drainage system that serves the north side of the Boise River. The Mill Slough conveys irrigation water that flows off agricultural fields known as return flow, stormwater from urban residential areas, and municipal wastewater discharged from the City of Star. The three-phase water quality improvement project, as conceived and developed by Dr. Jack Harrison with HyQual P.A., starts with construction of an automatic weir structure installed in the Mill Slough a short distance upstream from the Boise River.

The weir will increase the Mill Slough water level and form a small sediment settling basin. To prevent downstream spiraling of nutrients that collect in the settling basin, DD2 and the City will remove sediment and phosphorus from the basin.  The sediment will be sampled and removal rates tracked to demonstrate the effectiveness of this “in-channel” treatment.  Sediment and phosphorus removed from the settling basin will be applied to City-owned land. It is estimated the project will result in an average annual sediment load reduction to the Boise River of about 900 tons/year and a total phosphorus load reduction of about 365 pounds-P/yr.

In the next phase of the project, the phosphorous-rich water in Mill Slough would be diverted south over City-owned land using historic overland flow channels that drain to the river. The final phase of the project could include a higher level of water quality treatment via expanded riparian flow channels and newly constructed wetlands and/or treatment basins. Read the Mill Slough Water Quality Plan Description.

Mill Slough

Mill Slough in Middleton

To help finance the Project, the City and DD2 jointly applied for a matching grant of $172,500 from the Lower Boise Watershed Council (LBWC).  The LBWC was awarded $250,000 from the State of Idaho’s Agricultural BMP General Fund, and, on October 12, 2017, the LBWC approved a grant in the amount of $172,500 for the joint City/DD2 Project.