Water Quality Improvement Project
Liberty Lake Area:
Total Phosphorus


Liberty Lake is located near the Spokane River in the northeast portion of Washington State. The lake was made through glacial activity. The lake covers about 282 hectares and is about 5.5 meters deep. It is surrounded by hills on three sides. Land use in this area is mainly residential development, and is experiencing rapid growth.

The watershed, located over the Spokane-Rathdrum Prairie Sole-Source aquifer, is made up of shallow, permeable soils that rapidly drain over bedrock to the lake.

Water quality issues

In the mid 1960s Liberty Lake began to show symptoms of eutrophication. Eutrophication is the process in lakes when plant life, especially algae, begins to rapidly increase due to the abundance of mineral and organic nutrients.

Throughout the late 1960s and into the 1970s, large masses of decaying algae and plant fragments accumulated on the lake's beaches. Numerous sources were identified as contributors to nutrient enrichment of the lake, including a marshy area adjacent to the lake; unsewered homes near the lake; leaking sewer pipes; and stormwater. The marsh was an unusually high nutrient source, possibly because it was used as a manure spoils site in past years. Unsewered homes contaminated the ground water due to the unfavorable soils and geology of the area. Sewered areas had significant exfiltration, in which fluid leaks from the sewer pipeline into the surrounding soil. Stormwater runoff contributed nutrients picked up from surrounding land.

The lake sediments were found to be rich in nutrients. Due to the luxuriant growth of aquatic plants and algae, nutrients recycled in the lake.

Liberty Lake, eastern Washington State.  Photo courtesy of BCooner. Used by permission via Flickr..

© BCooner.

Why this matters

Excessive nutrient discharges into lakes encourage the rapid growth of aquatic plants and algae. Phosphorus and nitrogen are two nutrients commonly found in lakes. Excessive algae growth reduces water clarity. This lessens the amount of sunlight for other plants and aquatic life, killing them or limiting their growth. When algae die, they sink to the bottom of the lake and begin to decompose. Oxygen demand in the bottom sediments increases, as bacteria feed on this decomposing algae. This results in reduced dissolved oxygen (DO) levels in the lake, severely impacting coldwater aquatic habitat, and can, depending on the dominant algae present, pose a human health risk.

What was done

In 1968 the Liberty Lake Property Owner's Association requested water quality analyses. Results from early monitoring showed high nutrient levels, high chlorophyll a, and poor clarity. In 1973, the Liberty Lake Sewer District formed. The District identified two actions needed for lake improvement: sewering the lake drainage basin, and lake restoration work. Sewering of the drainage basin began and a lake monitoring/restoration plan was developed. Monitoring begun in the late 1970s.

In 1976, a sewer facilities plan was prepared and a sewer bond issue passed. In 1979, the wastewater collection system was completed and the lake restoration plan published. The restoration plan included dredging nutrient-rich sediments from the lake; application of alum; improving existing stormwater diversion structures; and the preparation of a storm water management plan.

Data from 1978-79 showed the marsh was the highest source of total phosphorus (TP). Diversion of flood flows around the marsh at south end of lake had the greatest effect on reducing TP loads to the lake, reducing them by 47 kilograms/yr (or from 7 percent to 1 percent of total TP budget by 1987). The restoration plan was implemented in 1981 and the lake monitored through 1983. A post-restoration analysis showed that nutrient loads in 1984 and 1985 were well below the TMDL goal.

Although Liberty Lake was not on Washington's 303(d) list of impaired waters, Ecology submitted a total maximum daily load (TMDL) for total phosphorus to EPA for approval as a federal Clean Lakes project. EPA approved the submittal in March 1993.

Status of the project

In 2008, Ecology evaluated the lake's water quality based on available data. Though inconclusive, the data suggested that the lake met water quality standards for phosphorus at that time.

Technical information

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

Liberty Lake Dataset Evaluation (Ecology Technical Memo)

Related information

Reducing Phosphorus Pollution to Improve Water Quality (Ecology website)

Liberty Lake: Finding Pollution Problems to Solve (Ecology water quality story)

Spokane River and Lake Spokane Dissolved Oxygen Total Maximum Daily Load: Water Quality Improvement Report (Ecology publication)

WRIA 57: Middle Spokane Watershed Information (Water website)


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Last updated June 2013
  Water resource inventory area (WRIA) 57 map, Washington State.


WRIA: #57 (Middle Spokane)
County: Spokane

Water-body Name:
Liberty Lake

Total Phosphorus

# of TMDLs: 1

Approved by EPA

Contact Info:
David T. Knight
Phone: 509-329-3590
Email: David.T.Knight@ecy.wa.gov

Eastern Region
Department of Ecology
4601 N. Monroe
Spokane, WA 99205-1295