E. Coli in the water? Over half of Idaho’s sewage treatment plants are polluting

BOISE (Idaho Statesman) — E. Coli and other fecal bacteria in rivers and lakes. Toxic metals, like lead, in Idaho waterways. Excessive nitrogen and phosphorus, leading to algae blooms that can kill fish and sicken people.

Idaho sewage treatment plants aren’t supposed to release pollutants like these into the water — but over half of them did last year, according to a recent report from the Idaho Conservation League.

More than half of those incidents — which violate the federal Clean Water Act — occurred in just 11 of the state’s more than 100 facilities, the report found. And some of the offending treatment plants have been breaking the law repeatedly for over a decade.

Treatment plants in Driggs, Preston and Plummer alone accounted for over 25% of all the violations last year, suggesting “significant structural or operational problems,” the Idaho Conservation League wrote.

It noted that in some cases, problems were on their way to being resolved. Preston, for example, completed an upgrade of its facility in late 2025 and has not reported any violations so far this year.

So far, violations haven’t resulted in dire consequences: There have been no major fish die-offs, and no reports of public health issues, Will Tiedemann, the organization’s regulatory program manager, told the Idaho Statesman.

“But it doesn’t mean there couldn’t be unseen consequences, or things that aren’t studied or being observed,” he said. Some of the pollutants entering Idaho’s water aren’t “acutely toxic” but can have effects that build up over time.

“It can be a slippery slope,” he said.

Mary Anne Nelson, who leads the Idaho Department of Environmental Quality’s Surface and Wastewater Division, told the Statesman that the department was aware of the plants that the Idaho Conservation League highlighted as repeat offenders, and said it “has taken or is taking appropriate compliance and enforcement actions” against those facilities.

She said she couldn’t share details about ongoing enforcement actions, as many of them were part of open enforcement cases. She noted that in 2022, the Environmental Protection Agency sued Driggs over its wastewater violations.

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Tiedemann noted that permit levels are intentionally set with some buffer, so that a violation doesn’t immediately cause a crisis.

But in a state that values aquatic life and being able to recreate in rivers and lakes, “we have to sometimes be more protective than what is acutely obvious,” he said. “We keep our waters cleanest by actively being diligent and adhering to our permits, not when we generally feel like, ‘OK, now it’s finally bad enough.’ ”

Across the state, Idaho has seen an uptick in harmful algae blooms since 2023, according to Idaho Conservation League data. In some bodies of water, including Lake Cascade and reservoirs on the Snake River, wastewater discharge may be driving the increase, Tiedemann said — though he noted that it’s one of several contributing factors.

Wastewater treatment plants in Nampa and Star reported zero violations in 2025, the report found. Of Boise’s two treatment plants, one reported zero violations in 2025; the other reported two.