Twin Falls Rock Creek Water Quality Plan Advances to Construction Phase After Two Years of Study
Master Plan Approved, Federal Funding Secured for Impaired Waterway
TWIN FALLS — After more than two years of water sampling, technical analysis, and community outreach, officials in Twin Falls are ready to move from planning to action on a long-running effort to restore water quality in Rock Creek.
Residents gathered on May 5 for an open house and public presentation on the Rock Creek Watershed Master Plan, a document representing nearly 1,000 pages of technical findings and project recommendations. City Assistant Manager Mandi Thompson noted the milestone, recalling that the process began with the first water samples collected just over two years ago.
“It is exciting to see it all come together,” Thompson said at Tuesday’s event.
The master plan has already received approval from the Twin Falls City Council, and the effort is backed by $5 million in federal funding. That financial foundation now positions the city to begin constructing the projects identified in the plan — a significant step forward after years of foundational study.
Environmental engineer Erin Day Cox of Jacobs Engineering explained that the open house marked not just a public information event, but a celebration of the research and documentation that made the construction phase possible. Cox said a user-friendly storyboard has been made available to help residents better understand the technical details of the water quality project without wading through dense scientific data.
“It’s really important to the people of this community,” Cox said, pointing to survey results and feedback gathered at public meetings. “There is overwhelming support for the project and vision.”
Springtime Runoff Among the Biggest Drivers of Pollution
Rock Creek has been designated an impaired waterway, and the data collected over the past two years shows that conditions deteriorate most significantly in the spring. As snowpack melts and runs off from the South Hills, topsoil — along with suspended solids, nutrients, and E. coli — washes into the creek before vegetation on surrounding fields has had a chance to establish and hold sediment in place.
More than 75 percent of survey respondents indicated they believe Rock Creek water quality falls below acceptable standards and needs improvement, according to Cox.
Based on the findings, proposed projects were organized into three categories: stormwater management, river corridor improvements, and agricultural practices. A ranking system identified the highest-priority projects from each category to receive first attention.
One of the top-priority stormwater projects is a bioretention facility near Shoshone Street South and Rock Creek. Cox said the facility would capture and treat 100 percent of runoff from roughly 47 acres of streets, parking lots, and urban areas draining into that zone. The design would slow the creek’s flow, allow sediment to settle to the bottom, and enable aquatic plant life to absorb nutrients — including phosphorus and nitrogen — before the water continues downstream into the Snake River “in much better condition,” Cox said.
Other projects in the plan target irrigation return flows and would employ technology such as carbon filters to capture pollutants before they reach the creek.
Lisa Love, a retired schoolteacher who attended Tuesday’s presentation, offered a personal perspective on why the creek matters to longtime residents. Love said she moved to Twin Falls in 1993 and took her five sons to Rock Creek Park to float the waterway with inner tubes. “We had so much fun down there,” she said, adding that city signage eventually warned visitors that entering the water was inadvisable due to water quality concerns.
Her experience reflects a broader community desire to reclaim Rock Creek as an accessible, safe recreational asset — something the master plan aims to deliver through a phased, science-driven approach.
Water quality efforts in Idaho have drawn increasing attention in recent years. A surface water coalition and groundwater districts reached a mitigation agreement that similarly underscored the importance of coordinated, data-backed approaches to protecting Idaho’s waterways. Meanwhile, municipalities across the state have been investing in infrastructure tied to their natural water corridors, including Pocatello’s Portneuf River bridge construction slated to move forward this spring.
What Comes Next
With the master plan approved and funding in place, Twin Falls officials are moving into the project construction phase. The city’s next steps will involve engineering and building out the priority projects identified in the master plan, beginning with high-impact stormwater interventions. Officials have indicated the storyboard resource will remain publicly available so residents can track progress as the work unfolds. No construction timeline was specified at Tuesday’s event, but the shift from study to implementation represents the most concrete progress the effort has made since water sampling began in early 2024.