Department of
Environmental Quality

Subbasin at a Glance

Overview

Black Lake, one of several lateral lakes along the Coeur d’Alene River, is approximately five miles west of Harrison, Idaho. The entire Black Lake watershed falls within Kootenai County, Idaho. Approximately two-thirds of the Black Lake watershed is located within the Coeur d’Alene Reservation, including the two southern arms of Black Lake. There are three primary tributaries draining to Black Lake: Porter Creek, Lamb Creek, and Black Creek. The land use/land cover in each subwatershed is primarily forested or used for agriculture. Only one percent of the Black Lake watershed has been developed.

A study of the physical, chemical, and biological conditions of Black Lake revealed that excess phosphorus in the lake is degrading water quality conditions by feeding nuisance aquatic plant growth that depletes oxygen important for fish. A beneficial use assessment demonstrated that it fails to support a viable aquatic life community for coldwater species and to support water quality conditions appropriate for recreational opportunities such as swimming.

To restore water quality in Black Lake, DEQ, the Coeur d’Alene Tribe and the U.S. Environmental Protection Agency (EPA) have developed a TMDL to reduce sources of phosphorus in the lake. Since beneficial use assessments have not been conducted on Porter Creek, Lamb Creek, or Black Creek, there are insufficient data to determine support or nonsupport of beneficial uses for these small streams. Thus, TMDLs were not written for the Black Lake tributaries.

For this TMDL, the Coeur d’Alene Tribe has agreed to apply Idaho’s water quality standards as the basis for establishing an appropriate water quality target for nutrients in Black Lake. The Coeur d’Alene Tribe, Region 10, and DEQ have agreed that the interpretation of the narrative criteria used in the TMDL will meet and protect the criteria and the designated uses of both the Coeur d’Alene Tribe and the state of Idaho for Black Lake.

Meeting the pollutant load allocations for phosphorus discussed in this TMDL will require the implementation of various policies, programs, and projects and the cooperation of various entities, including tribal, federal, state, and local governments, irrigation companies, and private individuals. Implementation strategies are described in the document below.

Subbasin Document

• Black Lake Watershed Assessment and Total Maximum Daily Load (March 2011)