Lake Tye Depth & Water Quality Testing

Lake Tye is a popular recreational lake located at the western edge of Monroe.  Throughout the year residents and visitors spend time at the lake swimming, paddling, fishing, and enjoying the surrounding park area.  

As required by the Washington State Department of Ecology, the City collects routine lake water samples to measure lake temperature, dissolved oxygen levels, and the current level of fecal coliform present in the water.  Watch the video to learn more about how our Environmental Services Division cares for Monroe’s waterways, including Lake Tye and Woods Creek. 

For questions or concerns regarding the water quality at Lake Tye, please visit submit your question, comment, or concern through Monroe Listens or 360-794-6100 during normal business hours.

Lake Depth

The Lake Tye water level fluctuates by approximately 3 feet seasonally. A bathymetric survey was done on the south half of the lake in 2012. At that time, the lake at its deepest point was approximately 29 feet. Certified city staff consistently monitors water levels to ensure the proper functioning and environmental health. The lake is approximately 40 acres in size. If you have any further questions or concerns, please visit Monroe Listens or call 360-794-6100 during normal business hours.

Water Quality Results

Fecal coliform bacteria are commonly found in streams and lakes. These bacteria are used as an indicator to help determine whether water may be contaminated by animal or human waste and could pose a health risk.

Low levels of fecal coliform are normal. However, when levels rise above 100 CFU per 100 milliliters of water, it may mean that other harmful germs could also be present. If testing at Lake Tye shows levels above 200 CFU per 100 milliliters, the City will notify the public.

If results exceed 200 CFU, the City will collect additional samples to decide whether further action is needed.

Heavy rain, especially the first rain after a dry period, can cause fecal coliform levels to increase. This happens when rain washes animal waste from streets, yards, and fields into nearby streams, lakes, and rivers.

MONTH/YR. JAN
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FEB
2026
MAR
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APR
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MAY
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JUNE
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DEC
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FECAL COLIFORM BACTERIA - CFU/100ML

30   12   4    4    2    4   4   16    14   6    38  680
Resample                       330

Lake Temperature is measured to predict the general health of the biological activity within the lake. If temperatures are exceedingly high, or low, fish, insects, zooplankton, phytoplankton and other aquatic species may be affected. As is to be expected, lake temperatures typically increase as the weather warms in the summer, and decrease as the weather cools in the winter.

MONTH/YR. JAN 
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FEB 
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TEMPERATURE - F

44.7   47.1 48.7 53.6 62.9 68.3 73.2 72.5  72.8 66.2  52.7  48.3 

Dissolved Oxygen is an important measure of water quality for aquatic life. When dissolved oxygen levels become low (less than 5 mg/l) aquatic life may suffer. Factors that may affect the level of dissolved oxygen in the lake include atmospheric pressure, water temperature, aquatic plant life cycle, ground water levels, and pollution in the water. For these reasons, it is normal for dissolved oxygen to fluctuate seasonally.

MONTH/YR. JAN
2026
FEB
2025
MAR
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APR
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MAY
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JUNE 
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JULY
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SEPT
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OCT 
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NOV
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DEC
2025
DISSOLVED OXYGEN - MG/L 10.7 12.8 12.7 13.4 11.9 10.3  10.1  8.84  9.9   7.8   7.3   9.1

Caution Blue-Green Algae

Blue-Green Algae is a potentially toxic type of bacteria (cyanobacteria) which is found in many of Snohomish County's lakes. Blue-green "blooms" are most commonly present when water temperatures are warmest in the summer months.

Protecting humans and pets by eliminating contact with and ingestion of blue-green tainted water is advisable.  If you become aware of a possible bloom, please report it to City staff so that an assessment and testing of the algae can be completed as necessary.