The U.S. Environmental Protection Agency (USEPA) approved a Total Maximum Daily Load (TMDL) for the Snake River-Hells Canyon reach ( ), which set seasonal (May through September) average and annual maximum concentrations of chlorophyll-a to preserve designated desirable uses that water quality should support, such as potable water supply, recreation, and aquatic habitat. To attain phosphorus concentration at the mouth of the Boise River has been set at 0.07 mg/L, which is lower than past monitored and modeled total phosphorus concentrations. However, interactions among and temporal variability in algae growth, nutrients, and other key water-quality parameters that may Boise River contributions of nutrients and algae to the loads transported by the Snake River into the Snake River-Hells Canyon reach.