Water Quality Improvement Project
Cottage Lake is located in King County and south Snohomish County, near
the city of Woodinville, Washington State. It's drainage area is
within the upper Bear Creek basin, which is a tributary to the Sammamish
River. The lake receives surface water from Daniels Creek,
including Crystal Lake, and Cottage Creek drainages. The lake also
receives water from surrounding land areas.
Water quality issues
For a number of years Cottage Lake experienced chronically elevated
phosphorus concentrations that have led to increased growth of algae (blooms)
during the summer months. Cottage Lake was listing on Washington State's
1996 and 1998 303(d)
lists for exceeding the state's water quality standards for total
phosphorus. These conditions undermined the beneficial uses of the lake
for activities such as fishing and swimming, and reduced Cottage Lake’s overall
aesthetic value and biological health.
Sources of phosphorus inputs into the lake included residential and
commercial development and maintenance, as well as animal husbandry.
Why this matters
Excessive nutrient inputs to lakes provide aquatic plant and algae dominance,
making lakes unsuitable for recreation or viewing enjoyment. Phosphorus
is one of the nutrients. When it is discharged into a waterbody, like a lake,
it fuels the growth of algae.
Excessive algae growth reduces water clarity, increases oxygen demand in the
bottom sediments severely impacting coldwater aquatic habitat, and can,
depending on the dominant algae present, pose a human health risk.
Status of the project
The Department of Ecology (Ecology), with help from local citizens, developed
a Total Maximum Daily Load (TMDL). Ecology submitted the finalized report
to EPA, which approved it on September 2004. Ecology then developed a more
detailed implementation plan, which was submitted to EPA in 2006.
Cottage Lake Total Maximum Daily Load Analysis: Submittal Report (Ecology publication)
Total Phosphorus Total Maximum Daily Load Water Quality Implementation
Plan (Ecology publication)
Cottage Lake: Watershed Education Helps
to Protect a Valuable Resource (Ecology publication)
WRIA 8: Cedar-Sammamish Watershed Information (Environmental Assessment
Program web site)
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Last updated May
# of TMDLs: 1
Approved by EPA
Has an implementation plan
Department of Ecology
3190 160th Ave. SE
Bellevue, WA 98008-5452