Sullivan Lake Water Temperature
Sullivan Lake in Morrison County, Minnesota averages about 65°F at the surface in summer — warmest in Aug (~67°F) and coldest in May (~56°F). These are typical values by month, not a live reading.
Typical water temperature by month
Typical surface water temperature by month, from 181 field readings (2016–2025) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Sullivan Lake warm enough to swim?
Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Want more than temperature? Sullivan 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 ~57°F
Summer average ~72°F
Summer average ~73°F
Summer average ~65°F
Summer average ~64°F
Summer average ~73°F
Explore water temperatures
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Frequently asked questions
What is the water temperature of Sullivan Lake?
Sullivan Lake has a typical summer surface temperature of about 65°F. It is usually warmest in August (around 67°F) and coldest in May (around 56°F). These are typical values by month from 181 EPA Water Quality Portal field readings (2016–2025), not a live reading.
When is Sullivan Lake warmest?
Surface water at Sullivan Lake is typically warmest in August, reaching about 67°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 Sullivan Lake warm enough to swim?
At its typical summer peak of about 65°F, Sullivan Lake rates as "cool" for swimming. Brisk but swimmable for short dips — most people acclimate after the first few minutes.
Where does this Sullivan 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 — 181 readings from 2 monitoring stations between 2016 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.