| Data | Details |
|---|---|
| Hydrologic Unit Codes | 17050123 |
| Size | 927 square miles (593,551 acres) |
|
Water Bodies with EPA-Approved TMDLs (Category 4a) |
Big Creek, Boulder Creek, Boulder/Willow Creek, Cascade Reservoir, Clear Creek, Fall Creek, Gold Fork, Mud Creek, North Fork Payette River, Round Valley Creek, tributaries to Payette Lake, West Mountain tributaries to Cascade Reservoir |
| Beneficial Uses Affected | Domestic water supply, agricultural water supply, cold water aquatic life, salmonid spawning, primary and secondary contact recreation |
| Major Land Uses | Agriculture, forestry, urban/suburban |
| Dates Cascade Reservoir TMDL Approved by EPA | Phase I: May 1996 | Approval Letter Phase II: April 1999 | Approval Letter |
| Date Payette/North Fork Payette TMDL Approved by EPA | August 2005 Approval Letter |
| Date Tributary TMDL Addendum Approved by EPA | February 2012
Approval Letter |
Subbasin Characteristics
The North Fork Payette River subbasin lies on the northern edge of the Southwest Basin and encompasses the towns of McCall, Donnelly, and Cascade. The subbasin includes Cascade Reservoir and the Payette Lakes.
1996 and 1999 Cascade Reservoir Watershed Assessment and TMDL
Cascade Reservoir is located in the North Fork Payette River subbasin of southwestern Idaho (hydrologic unit code 17050123). 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). The watershed is approximately 558 square miles (357,000 acres).
Cascade Reservoir is a shallow water body that 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 water quality 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 (completed in June 2000)
Phase III
Plan evaluation and modification (completed in February 2009).
1996 and 1999 TMDLs: Subwatersheds and Pollutants for Which TMDLs Were Developed
Phase 1
| Stream | Pollutants |
|---|---|
| Boulder Creek | Phosphorus |
| Cascade Reservoir | Phosphorus |
| Gold Fork River | Phosphorus |
| Lake Fork Creek | Phosphorus |
| Mud Creek | Phosphorus |
| North Fork Payette River | Phosphorus |
| West Mountain tributaries | Phosphorus |
| Willow Creek | Phosphorus |
| Boulder Creek | Phosphorus |
Phase II
| Stream | Pollutants |
|---|---|
| Boulder/Willow Creeks | Phosphorus |
| Cascade Reservoir | Phosphorus |
| Gold Fork River | Phosphorus |
| Lake Fork Creek | Phosphorus |
| Mud Creek | Phosphorus |
| North Creek | Phosphorus |
| West Mountain tributaries | Phosphorus |
2005 Payette River and North Fork Payette River Watershed Assessment and TMDL
This watershed spans two subbasins, as summarized in the table below.
| Data | Details |
|---|---|
| Hydrologic Unit Codes | 17050122 (Payette) and 17050123 (North Fork Payette) |
| Size | 2,152 square miles (1,377,280 acres) |
| Beneficial Uses Affected | Cold water aquatic life, salmonid spawning, primary contact recreation, domestic water supply |
| Major Land Uses | Agriculture, forest, range, municipalities |
The Payette River watershed lies entirely in southwestern Idaho and comprises about 3,240 square miles in two different subbasins. The drainage originates in the Sawtooth and Salmon River Mountains and flows southwesterly until it empties into the Snake River near Payette, Idaho.
This TMDL lies within parts of two hydrologic units and encompasses several geographically distinct subwatersheds. This TMDL addresses §303(d)-listed tributaries to the North Fork Payette River above Payette Lake and to Payette Lake itself; the North Fork Payette River and tributaries from Cascade Dam to the confluence with the South Fork Payette River; and the main stem Payette River up to and including Black Canyon Reservoir.
The North Fork Payette River is listed for nutrients, sediment, and temperature. Beneficial uses are not impaired by nutrients, so nutrients are recommended for delisting. Temperatures exceed the temperature standard, primarily due to warm water exiting Cascade Reservoir. Canopy cover meets target levels, so a TMDL was not developed for temperature. A TMDL for sediment was developed.
Big Creek is listed as impaired by sediment and data show that beneficial uses are impaired. Banks are stable in some sections but actively eroding in others. A TMDL was developed for sediment. In Round Valley Creek, beneficial uses are impaired due to excess sediment from instream channel erosion. A TMDL was developed.
Temperature TMDLs were developed for Box Creek and Fall Creek in order to achieve salmonid spawning criteria. The streams support beneficial uses but do not meet the salmonid spawning standard.
Beneficial uses are not supported in the lower reach of Clear Creek due to excess sediment from upstream and instream channel erosion. In the upper reaches of Clear Creek, beneficial uses are fully supported but are threatened due to excess sediment. A sediment TMDL was set for the upper watershed to improve habitat in the lower reaches.
Browns Pond is listed for habitat alteration. However, habitat alteration is not considered a “pollutant,” and TMDLs are not required for pollution that is not caused by a pollutant. Therefore, a TMDL for Browns Pond was not developed.
Soldier Creek is listed for sediment. DEQ proposes delisting Soldier Creek from the headwaters to the confluence with North Fork Soldier Creek but leaving the lower section of Soldier Creek on the §303(d) list. DEQ will use data gathered in 2005 to determine whether sediment is impairing beneficial uses in the lower section. Tripod Creek was preliminarily found to be unimpaired and a TMDL is not recommended at this time. Additional monitoring data will become available in 2005, which may result in further study of Tripod Creek and TMDL development.
It is proposed that Brush Creek, Elip Creek, and Landing Creek be removed from the §303(d) list and that Black Canyon Reservoir be delisted for nutrients, sediment, and oil and grease but listed for habitat alteration. It is also proposed that Squaw Creek be added to the next §303(d) list for bacteria and nutrients.
2005 TMDL: Streams and Pollutants for Which TMDLs Were Developed
| Big Creek | Sediment |
| Box Creek | Temperature |
| Clear Creek | Sediment |
| Fall Creek | Temperature |
| Round Valley Creek | Sediment |
| North Fork Payette River | Sediment |
2011 Cascade Reservoir Addendum
This addendum addresses assessment units (AUs) found to be impaired during the Cascade Reservoir watershed five-year review and placed on Idaho’s 2010 §303(d) list for sediment. DEQ developed sediment TMDLs for three water bodies (four AUs). Sediment targets of 80% bank stability were chosen to bring these water bodies into compliance with Idaho’s narrative sediment criterion.
2011 Addendum: Streams and Pollutants for Which TMDLs Were Developed
| Gold Fork River | Sediment |
| Boulder Creek | Sediment |
| Mud Creek | Sediment |
Subbasin Document(s)
- Implementation Plan for the Cascade Reservoir Phase II Watershed Management Plan
- North Fork Payette River Subbasin Assessment and Total Maximum Daily Load
- North Fork Payette River Watershed TMDL Implementation Plan
- North Fork Payette River Watershed TMDL Five-Year Review
- Cascade Reservoir Phase I Watershed Management Plan
- Cascade Reservoir Phase I Watershed Management Plan Appendices
- Cascade Reservoir Phase II Watershed Management Plan
- Cascade Reservoir Phase II Watershed Management Plan Appendices
- Cascade Reservoir Watershed Phase III Water Quality Management Plan and TMDL Five-Year Review
- Cascade Reservoir Tributary TMDL Addendum
- Cascade Reservoir Watershed: TMDL Five Year Review
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