Lake Langlois

Vital Statistics
Overview
Maps
Water Quality Data
Reports and Related Links

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Vital Statistics

Watershed Area	226 acres
Lake surface area	39 acres
Maximum depth	98 feet
Mean depth	53 feet
Public Park	N
Boat Ramp	Y, no gas engines
Fish Present	stocked rainbow, kokanee

Overview

Volunteers monitored Lake Langlois from 2001-2008, 2014-2015, 2019-2020 and resumed again in 2024.

The key takeaways from the 2024 monitoring season are:

• Langlois Lake continues to have very clear water, with low nutrient concentrations and low algal growth. • While lake monitoring has not been consistent over the years, long-term trends suggest that water quality in Lake Langlois has been improving over time, with decreasing nitrogen concentrations. • Nitrogen-to-phosphorus (N:P) ratios were above 25 for most of the monitoring season. This indicates a low likelihood for the algal community to be dominated by cyanobacteria (which have the ability to produce toxins). • No algal blooms were reported for toxin testing in 2024.

Maps

This bathymetric map shows contour lines of equal depth, similar to a topographic map would for mountains and valleys. The red 'X' marks the location where water quality samples are taken.

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

Water Quality Data

Through a combination of efforts by volunteer lake monitors and King County staff, data relating to physical, chemical, and biological aspects of the lake have been collected for most lakes. The King County Lake Stewardship Program analyzes data to track long-term water quality trends in small lakes in western King County.

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 for a single water year at a time.

Water quality over time
A common method of tracking water quality trends in lakes is by calculating the “trophic state index” (TSI) (Carlson, 1977) and testing the values for positive or negative trends over time. TSI indicators predict the biological productivity of the lake based on water clarity (Secchi) and concentrations of total phosphorus (TP) and chlorophyll a (Chlor). Generally at least 8 years of data without major lake management activities are needed to have confidence in a significant trend.

The average of these three TSI indicators during the growing season can be used to place lakes in one of three broad categories:
<40 = oligotrophic (low productivity),
40 to 50 = mesotrophic (moderate productivity)
>50 = eutrophic (highly productive).

Reports and Related Links

2024 Water Quality Plot
2020 Lake Langlois Monitoring Report
2019 Lake Langlois Monitoring Report

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For questions about lakes in King County, please contact lakes@kingcounty.gov or call the Water and Land Resources Division front desk at 206-477-4800.