Rainy Lake Water Temperature
Rainy Lake in Cass County, Minnesota typically sits around 68°F at the surface in September — warmest in Aug (~69°F) and coldest in May (~52°F). That is a typical value for the month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 90 field readings (2023–2024) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Rainy Lake warm enough to swim?
Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Want more than temperature? Rainy 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 ~72°F
Summer average ~74°F
Summer average ~74°F
Summer average ~74°F
Summer average ~64°F
Summer average ~68°F
Explore water temperatures
Where to stay near Rainy Lake
Planning a swim or lake trip? Compare cabins, lodges, and vacation rentals near Rainy Lake — live availability and prices. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Rainy Lake
Prices for Sep 4–6, 4 adults. Change dates on the map below.
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Frequently asked questions
What is the water temperature of Rainy Lake?
Rainy Lake typically sits around 68°F at the surface in September, from 90 EPA Water Quality Portal field readings (2023–2024). That is a typical value for the month, not a live reading.
When is Rainy Lake warmest?
Surface water at Rainy Lake is typically warmest in August, reaching about 69°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 Rainy Lake warm enough to swim?
At its typical summer peak of about 66°F, Rainy Lake rates as "cool" for swimming. Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Where does this Rainy 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 — 90 readings from 1 monitoring station between 2023 and 2024. 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.