Cascade Reservoir

Subbasin at a Glance

Hydrologic Unit Codes	17050123
Size	357,000 acres
§303(d) Listed Stream Segments	Cascade Reservoir, Mud Creek, Boulder Creek, Gold Fork River, Brown's Pond, Campbell Creek, French Creek, Hazard Creek, Lake Fork Creek, Willow Creek, Duck Creek, VanWyck Creek
Beneficial Uses Affected	Domestic water supply, agricultural water supply, cold water biota, salmonid spawning, primary and secondary contact recreation, special resource water
Pollutants of Concern	Nutrients (phosphorus), pathogens, ammonia, sediment, temperature, flow alteration, habitat alteration, dissolved oxygen, pH
Major Land Uses	Agriculture, forestry, urban/suburban
Dates Approved by U.S. EPA	Phase I: May 1996 Phase II: April 1999
Tributary TMDL Addendum Approved by U.S. EPA	February 2012 EPA Approval Letter

Overview

Cascade Reservoir is located in the Payette River Basin of southwestern Idaho. Two rivers (North Fork Payette River and Gold Fork River) and four creeks (Mud Creek, Lake Fork Creek, Boulder Creek, and Willow Creek) all discharge into the northern end of the reservoir. The watershed includes two major drainages: the Big Payette Lake drainage area and the Cascade Reservoir drainage area (the area included in this management plan).

Cascade Reservoir is a shallow water body, and, as such, it is highly susceptible to eutrophication due to nutrient loading and elevated summer water temperatures. Eutrophication was especially apparent in 1993 and 1994 when dense mats of blue-green algae were present in the reservoir. Twenty-three cattle died in 1993 after ingesting toxins produced by the algae and a substantial fish kill occurred in 1994.

Cascade reservoir has been identified as water quality limited due to violations of water quality standards for dissolved oxygen, temperature, and pH. Elevated levels of phosphorus directly contribute to these violations. To improve the quality of water in Cascade Reservoir and its tributaries, the current contribution of phosphorus from external sources must be reduced by 37%, and this reduction must be maintained for at least five years.

The plan developed for achieving water quality improvements in Cascade Reservoir includes three phases and an implementation plan:

Phase I: Initial nutrient reduction goal and implementation strategy (approved by EPA in May 1996).
Phase II: Further evaluation of phosphorus reduction goals and alternatives (approved by EPA in April 1999).
Implementation Plan: A subwatershed-specific outline of projects that have been and will be initiated to effect required water quality improvements within Cascade Reservoir.
Phase III: Plan evaluation and modification (underway).

Subwatersheds and Pollutants for Which TMDLs Were Developed

Phase I

Boulder Creek: Phosphorus
Cascade: Phosphorus
Gold Fork River: Phosphorus
Lake Fork Creek: Phosphorus
Mud Creek: Phosphorus
N. Fork Payette River: Phosphorus
West Mountain: Phosphorus
Willow Creek: Phosphorus
Boulder Creek: Phosphorus

Phase II

Boulder/Willow: Phosphorus
Cascade: Phosphorus
Gold Fork: Phosphorus
Lake Fork: Phosphorus
Mud Creek: Phosphorus
North Creek: Phosphorus
West Mountain: Phosphorus

Subbasin Documents

Cascade Reservoir Phase 1 Watershed Management Plan (January 1996)
Cascade Reservoir Phase 1 Watershed Management Plan Appendices (January 1996)
Cascade Reservoir Phase 2 Watershed Management Plan (December 1998)
Cascade Reservoir Phase 2 Watershed Management Plan Appendices (December 1998)
Cascade Reservoir Watershed Phase III Water Quality Management Plan and TMDL Five-Year Review (February 2009)
Cascade Reservoir Tributary TMDL Addendum (November 2011)

Department of
Environmental Quality

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