Mary Lake Water Temperature
Mary Lake in Douglas County, Minnesota averages about 71°F at the surface in summer — warmest in Jul (~76°F) and coldest in Sep (~67°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 18 field readings (2010–2021) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Mary Lake warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Want more than temperature? Mary Lake scored B on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
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Frequently asked questions
What is the water temperature of Mary Lake?
Mary Lake has a typical summer surface temperature of about 71°F. It is usually warmest in July (around 76°F) and coldest in September (around 67°F). These are typical values by month from 18 EPA Water Quality Portal field readings (2010–2021), not a live reading.
When is Mary Lake warmest?
Surface water at Mary Lake is typically warmest in July, reaching about 76°F. Lake surface temperature lags air temperature by several weeks, so the warmest water usually arrives in mid-to-late summer even though the hottest air can come earlier.
Is Mary Lake warm enough to swim?
At its typical summer peak of about 71°F, Mary Lake rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
Where does this Mary Lake water temperature data come from?
Every temperature on this page is a typical (climatological) value computed from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal — 18 readings from 2 monitoring stations between 2010 and 2021. They describe what is typical for each month, not the temperature right now.
About this data
Water temperatures are a climatology — the typical value for each month, averaged from real surface-water field readings collected by state and federal agencies and published through the EPA Water Quality Portal. They tell you what to expect, not the temperature at this moment. Actual conditions vary with recent weather, depth, and time of day.