Assessing the Water Quality of the Lower Boise River and Selected Tributaries

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For decades, the lower Boise River downstream of Lucky Peak Reservoir has been highly enriched with phosphorus. Too much of a good thing, the high concentrations of phosphorus create a cycle of excessive plant growth, decreased oxygen for fish, and even algal blooms. 

We have worked with the Idaho Department of Environmental Quality and the Lower Boise Watershed Council to monitor water quality in the Boise River since the 1970s. Together, we have designed a monitoring program to help determine the:

  • Status and trends of stream water quality in the Boise River near Parma, Middleton, and Eckert Road; 
  • Variability in sediment and phosphorus concentrations and loads in the Boise River near Parma annually and during short-duration events; 
  • Status and trends in total phosphorus and orthophosphate concentrations and loads in selected tributaries seasonally; and 
  • Seasonal variability in periphyton growth in the lower Boise River.

Most recently, we have collected water-quality samples six times per year from the Boise River between Star and Middleton, and from near Parma. These samples are analyzed for a variety of constituents, including phosphorus and other nutrients. Partnering with the City of Boise, we also use an automatic sampler to collect samples every 49 hours from the Boise River near Parma; these samples are analyzed for total phosphorus (phosphorus in all forms).