An extensive study was done in 2015 by Thurston County, the Thurston Regional Planning Council and the Environmental Protection Agency to guide growth in the Black Lake Basic Watershed. Stormwater runoff and faulty septic systems were found to be major contributors to poor water quality in the lake.
Algal blooms are a recurring and increasing problem in Black Lake. Black Lake Ditch, which drains the lake at its northern end, violates fecal coliform and dissolved oxygen standards.
Black Lake Basin Study, 2013-2015 Thurston County
Water Quality Problems Facing Black Lake
The main issue facing Black Lake is nutrient loading. The following list includes the primary sources of these nutrients.
- Failing onsite sewage systems. This occurs primarily in the drain field but could be the septic tank as well.
- Stormwater runoff from pasture lands in the creeks that drain into Black Lake.
- Stormwater runoff from residential lots.
- Stormwater runoff from roads and other developments.
- Stormwater runoff from undeveloped land.
Stormwater runoff can cause water quality problems whether it is directly into Black Lake, or into one its tributaries. Stormwater solutions need to address the entire Black Lake watershed, all of the land that where rainwater will eventually end up in Black Lake.