Long Lake Water Temperature
Long Lake in Lake County, Illinois typically sits around 74°F at the surface in September — warmest in Jul (~80°F) and coldest in Feb (~38°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 177 field readings (2012–2024) via the EPA Water Quality Portal. Months with too few readings are left blank.
Is Long Lake warm enough to swim?
Pleasant for swimming — the range most people find enjoyable without a wetsuit.
A live gauge on Long Lake last read 83°F. See the full Long Lake water-quality page for current conditions and readings.
Want more than temperature? Long Lake water quality: clarity, algae, phosphorus, depth, fish species, and current advisories, all on one page.
Water temperatures at nearby Illinois lakes
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Where to stay near Long Lake
Planning a swim or lake trip? Compare cabins, lodges, and vacation rentals near Long 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 Long Lake
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Frequently asked questions
What is the water temperature of Long Lake?
Long Lake typically sits around 74°F at the surface in September, from 177 EPA Water Quality Portal field readings (2012–2024). That is a typical value for the month, not a live reading. A USGS gauge on this lake last read 83°F.
When is Long Lake warmest?
Surface water at Long Lake is typically warmest in July, reaching about 80°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 76°F, Long Lake rates as "comfortable" for swimming. Pleasant for swimming — the range most people find enjoyable without a wetsuit.
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 — 177 readings from 2 monitoring stations between 2012 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.