Phosphorus Removal Facility

The Phosphorus Removal Facility is a precedent-setting and innovative project that will greatly enhance water quality of the Boise and Snake Rivers by removing up to 140 pounds of phosphorus per day from water flowing downstream.


A critical component of the health of the Boise River is its nutrient makeup. One of those nutrients is phosphorus, which at normal levels is a key part of the river’s water quality. However, high amounts of phosphorus can produce algae blooms that have negative impacts on overall water quality, fish and other aquatic animals.

Upcoming regulations will require a 98% reduction in the amount of phosphorus leaving the City of Boise’s treatment facilities into the lower Boise River. Boise is currently making improvements at its facilities to remove about 93% of phosphorus through its treatment plants, which protect the upper stretch of the river. The remaining five percent of phosphorus to be removed would require very expensive modifications to existing city facilities and miss an opportunity to remove great amounts of phosphorus otherwise untouched.

Aerial of Phosphorus Removal Facility

Instead, the City of Boise and its partners devised a ground-breaking approach that would result in even better overall water quality for the Boise and Snake Rivers.

A new phosphorus removal facility was built at an agricultural drain near the confluence of the Boise and Snake rivers with the goals of:

  • Improving water quality by removing up to ten tons of phosphorus per year from treated water flowing downstream
  • Proactively meeting upcoming water quality regulations
  • Ensuring the greatest environmental return on investment

Through the treatment efforts both upstream at the existing treatment plants and downstream at the Phosphorus Removal Facility, the overall environmental benefit to the river system is greatly improved.


Environmental Return on Investment

For the same cost as upgrading facilities at the existing treatment plants, this project removes much more phosphorus from the Boise and Snake Rivers. Essentially, for every pound that is not removed at a treatment facility in Boise, a pound and a half is removed downstream at the Phosphorus Removal Facility.

Phosphorus Otherwise Untouched

The Phosphorus Removal Facility captures ground and surface water flows coming from agriculture operations. These discharges are unregulated and are estimated to contribute up to 40% of the total phosphorus flowing from the Boise and Snake rivers. If it were not for this project, this significant phosphorus discharge would otherwise remain untouched.

Common Sense Location

Approximately 80% of the water treated at Boise’s treatment plants is diverted downstream for irrigation. With this project, the phosphorus is removed at a location where there are no further diversions for irrigation and additional loading of phosphorus.

Added Benefit

In addition to phosphorus being removed from the rivers, sediment levels are also greatly reduced, improving not only river aesthetics, but improving habitat for fish and aquatic life.

Lasting, Innovative and Vibrant

Lasting environments and vibrant communities will take continued collaboration and innovation. Eight years in the making, the Phosphorus Removal Facility serves as an important milestone and example of what dedication, hard work and partnership can accomplish.

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