Long Lake Water Temperature
Long Lake in Cass County, Minnesota averages about 53°F at the surface in summer — warmest in Jun (~54°F) and coldest in May (~47°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 499 field readings (2011–2025) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Long Lake warm enough to swim?
Wetsuit territory. Brief exposure is tolerable but prolonged swimming without protection risks hypothermia.
Want more than temperature? Long Lake scored A on water quality — clarity, algae, phosphorus, depth, fish species, and swimming safety, all on one report card.
Water temperatures at nearby Minnesota lakes
Summer average ~62°F
Summer average ~65°F
Summer average ~71°F
Summer average ~68°F
Summer average ~65°F
Summer average ~66°F
Explore water temperatures
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Frequently asked questions
What is the water temperature of Long Lake?
Long Lake has a typical summer surface temperature of about 53°F. It is usually warmest in June (around 54°F) and coldest in May (around 47°F). These are typical values by month from 499 EPA Water Quality Portal field readings (2011–2025), not a live reading.
When is Long Lake warmest?
Surface water at Long Lake is typically warmest in June, reaching about 54°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 Long Lake warm enough to swim?
At its typical summer peak of about 53°F, Long Lake rates as "cold" for swimming. Wetsuit territory. Brief exposure is tolerable but prolonged swimming without protection risks hypothermia.
Where does this Long 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 — 499 readings from 2 monitoring stations between 2011 and 2025. 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.