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Lake Washington photo

Physical Characteristics

Drainage Area (including Mercer Island) 357,760 acres (559 miles2) 1,448 km2
Lake Area 21,500 acres 87.6 km2
Lake Volume 2,350,000 acre-ft 2.9x109 m3
Mean Depth 108 feet 32.9 m
Maximum Depth 214 feet 65.2 m
Flushing Rate 0.43 per year
Length 22 miles 35 km
Main Inflows Cedar River (57%) Sammamish River (27%)
Main outlet Ship Canal to Puget Sound
Typical period of stratification Late March to early November
Trophic state mesotrophic

Monitoring Overview

Lake Washington is the largest of the three major lakes in King County, and the second largest natural lake in the state of Washington. Learn more about the history of the lake and water quality monitoring efforts by reading the Lake Washington Story.

King County currently has four sampling stations located in Lake Washington; Station 0804 in the north near the mouth of the Sammamish River, Station 0852 in the deep basin near I-520, Station 0826 mid-lake off Sand Point, and Station 0831 in the south end near the mouth of the Cedar River. Station 0852 is the legacy station that the University of Washington began monitoring in 1993. The other stations have been monitored since the early 1980s. In addition, sampling stations located around the shoreline of the lake, mostly near influent streams, were sampled from the mid-1980s until the program reduction in 2009. Samples are collected twice monthly from March through November, and once monthly from December through February. There is also a monitoring buoy located in the central basin of the lake that collects continuous temperature, pH, oxygen, conductivity, chlorophyll-a, and turbidity readings throughout the water column, as well as weather information.

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Water Quality Data

View or Download Data

Use this tool to view or download data from the lake in tabular format. You can define date ranges and select which parameters to view or download.

Chart Data

Use the charting tool to look at graphs showing single parameters.

Data Map

Choose a sampling location on the map to view or download data.

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