Water Quality Improvement Project
Wapato Lake Area:
Total Phosphorus


Wapato Lake is located in Wapato Park in southeast Tacoma, Washington. The lake covers 28 acres. It is known for fishing, especially for anglers under the age of 15.

Water quality issues

Phosphorus levels in Wapato Lake violated state water quality standards for total phosphorus. Noted lake issues included blue-green algae blooms; low dissolved oxygen; turbidity; sediment phosphorus recycling; and fecal coliform bacteria.

Algae continue to be a problem in the lake, along with high concentrations of phosphorus due to runoff from streets and yards surrounding the lake. The lake is also listed on the state's 303(d) list of impaired waters for fecal coliform.

© Tiffany Collier Withrow, Flickr.

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 water body, 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

Ecology developed a total maximum daily load (TMDL) study and submitted it to the Environmental Protection Agency (EPA). EPA approved the TMDL in April 1993.

The primary purpose for restoring water quality in Wapato Lake was to meet water quality standards for recreational uses while enabling its continued use as a winter stormwater detention facility. Implementation measures included applying alum treatments to precipitate/inactivate phosphorus in the water; divert stormwater to a wetland; dilute/flush lake water; drawdown water levels in the lake; apply stormwater controls; and educate the public about phosphorus issues. Of the measures used, the ones that produced the most significant results were stormwater diversion to a wetland; and alum treatments.

Technical information

Wapato Lake Total Phosphorus Total Maximum Daily Load (Ecology publication)

Related information

Lake restoration and management for algae

WRIA 12: Chambers-Clover Watershed Information (Water web site)


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Last updated November 2015
  Water Resource Inventory Area (WRIA) 12 map, Washington State.


WRIA: #12 (Chambers-Clover)
County: Pierce

Water-body Name:
Wapato Lake

Total Phosphorus

# of TMDLs: 1

TMDL approved by EPA

Contact Info:
Donovan Gray
Phone: 360-407-6407
Email: Donovan.Gray@ecy.wa.gov

Southwest Region
Department of Ecology
P.O. Box 47775
Olympia, WA 98504-7775