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Lake Samammish photo

Physical Characteristics

Watershed Area 63,000 acres (98 miles2) 255 km2
Lake Surface Area 4,897 acres 19.8 km2
Lake Volume 283,860 acre-ft 3.5x108 m3
Mean Depth 58 ft 17.7 m
Maximum Depth 105 ft 32 m
Flushing Rate 0.56 per year
Length 8 miles 12.9 km
Main Inflow Issaquah Creek
Main Outlet Sammamish Slough
Typical Period of Stratification mid-May to mid-November
Trophic State mesotrophic

Monitoring Overview

Lake Sammamish is the sixth largest lake in Washington and the second largest in King County. It is one of the major recreational lakes, with high use by fishermen, boaters, water skiers, swimmers, and picnickers. There are both State and County parks along the shore, and the lake has been designated a Water of Statewide Significance. Learn more about the history of the lake and water quality monitoring efforts by reading the Lake Sammamish Story.

King County has two sampling stations located over the deep central basin of Lake Sammamish, where the influence of the shoreline is muted by the surrounding water and mixing action of wind and waves. Station 0612 in the central basin has been sampled by King County since 1979. Station 0611 in the northern basin has been sampled since 1994. 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 southern basin of the lake that collects continuous temperature, pH, oxygen, conductivity, chlorophyll, and turbidity readings through the lake 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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Lake Management Goals

The Lake Sammamish Water Quality Management Plan (King County 1996) reviewed the ways that point and non-point pollutant loading were impacting the lakes and streams in the Sammamish watershed, as well as identifying some proposed methods for addressing the problems. The Plan identified three annual goals using water clarity (Secchi disk transparency), chlorophyll-a (a measure of algal biomass) and total phosphorus (important nutrient for algal growth).

  • Mean summer (June - September) transparency of 4.0 meters or greater measured at mid-lake stations 0611 and 0612,
  • Mean summer (June - September) chlorophyll-a concentrations of 2.8 µg/L or less,
  • Annual mean volume weighted total phosphorus concentration of 22 µg/L or less.

Sammamish TP Sammamish Chl Sammamish Secchi

*As per the 1996 Lake Sammamish Water Quality Management Plan.

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Lake Elevation

USGS maintains a lake level gage near the city of Redmond. You can view a graph with daily lake level readings at their web site.

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bathymetric map lake watershed map
This bathymetric map shows contour lines of equal depth, similar to a topographic map would for mountains and valleys. This map shows the area of the watershed relative to the area of the lake. Generally speaking, the larger a watershed is relative to a lake, the greater the influence land use practices on lake water quality.

Click image to enlarge