Idaho Water Science Center
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Water-Quality and Biological Trends on the
Lower Boise River

Conducted in cooperation with Idaho Department of Environmental Quality
USGS personnel collecting samples from the lower Boise River

Background

Between 1990 and 2005, Ada and Canyon County population increased nearly 60% to 509,320, and is expected to continue growing over the next ten years*. The lower Boise basin contains the most industrialized and urbanized areas in Idaho.

Within the last century, the lower Boise River has been transformed from a meandering, braided, gravel-bed river that supported large runs of salmon to a channelized, regulated, urban river that provides flood control and irrigation to over 1,200 mi2 of land.

Several lower Boise River tributaries are interconnected by a complex irrigation system of canals, laterals, and drains. Flow in the lower Boise between Lucky Peak Dam and the mouth is primarily controlled by reservoir regulation; irrigation withdrawals and return flows; and seepage of shallow ground water. Three upper basin reservoirs have a combined storage capacity of approximately 1 million acre-ft. These reservoirs are primarily managed for irrigation and flood control, and secondarily for recreation and power generation.

The water quality and biotic integrity of the lower Boise River between Lucky Peak Dam and the river's mouth near Parma, Idaho, have been adversely affected by many factors:

  • Urban and residential development
  • Agricultural land and water use
  • Wastewater-treatment facility discharge
  • Road construction
  • Urban runoff
  • Confined-animal feeding operations
  • Reservoir operations
  • River channelization
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In 1992 the lower Boise River Watershed Council (LBWC) was formed to identify nutrient and suspended sediment sources; initiate voluntary water-quality management practices; and monitor the long-term effectiveness of these practices on the river's water quality and biotic integrity.

In October 1994, the lower Boise River and some of its tributaries were listed as water-quality limited in accordance with paragraph 303(d) of the Clean Water Act (U.S. Environmental Protection Agency, 1994). Beneficial uses and pollutants for each segment are:

Lower Boise River Segments Diversion Dam to Star Star to Notus Notus to Snake River
Pollutants
Sediment
X
X
X
Dissolved oxygen
X
X
X
Oil and grease
X
 
 
Nutrients
 
X
X
Temperature
 
X
X
Bacteria
 
X
X
Beneficial Uses
Domestic water supply
X
 
 
Agricultural water supply
X
X
X
Coldwater biota
X
X
X
Salmonid spawning
X
X
 
Primary contact recreation
X
X
X
Secondary contact recreation
X
 
X

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*http://factfinder.census.gov—April 2006