Polk County restores 11 streams in $17M water quality push
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Before-and-after aerial views show stream restoration work near Ankeny aimed at reducing erosion and improving water quality. Photos: Courtesy of Polk County Public Works
A $17 million project to repair stream erosion is nearing completion in Polk County.
Why it matters: The investment could serve as a blueprint for the rest of the state's waterways if researchers can demonstrate measurable water quality improvements.
Catch up quick: Polk County launched the initiative in 2024, with the first restoration projects starting in 2025.
- It covers 11 stream restoration projects spanning nearly 10 miles in Ankeny, Altoona, Mitchellville, Des Moines and Pleasant Hill.
Context: The work comes amid years of water quality concerns, including high nitrate levels that prompted the metro's first mandatory lawn-watering ban in 2025.
By the numbers: Costs have fallen by about $4 million from the county's previously reported $21 million estimate, thanks to competitive construction bidding, Polk County water resources supervisor John Swanson tells Axios.
- Six projects are complete, two are expected to finish in November, and three are scheduled for completion in spring 2027.
Follow the money: The state is covering about 63% of the total costs ($10.62 million), with Polk County, participating cities and other local partners paying the remainder, according to county records.
How it works: Crews stabilize eroding streambanks and restore natural features to help prevent soil and sediment from washing downstream.
- Polk County is partnering with local governments, the Iowa Department of Agriculture and Land Stewardship and other organizations, Swanson said.
Case in point: Restoration at Thomas Mitchell Park near Mitchellville earned statewide engineering and public works awards this year.
Between the lines: The environmental benefits haven't yet been quantified.
- Iowa State University researchers are monitoring erosion, water quality and ecological conditions along Fourmile Creek in Ankeny.
- The study, which began in 2024 and runs through 2028, will measure changes before and after restoration.
What's next: Crews will complete the remaining construction and spend the next two years establishing prairie vegetation at restoration sites.