Illinois Lake Water Temperatures
Typical surface water temperatures for 90 Illinois lakes — about 72°F in September. Slm Side Channel Lake runs warmest (~86°F in summer); the statewide summer average is about 76°F. Values are typical by month, not live readings.
90
Lakes with a temperature record
72°F
Typical in September
76°F
Typical summer average
86°F
Warmest: Slm Side Channel Lake
Illinois lakes by typical summer water temperature (warmest first)
| Lake | County | Typical in September | Summer avg | Warmest | Coldest |
|---|---|---|---|---|---|
| Slm Side Channel Lake | St. Clair | — | 86°F | 88°F (Jul) | 63°F (Apr) |
| Sam Dale Lake | Wayne | — | 85°F | 88°F (Aug) | 65°F (Oct) |
| Coulterville Lake | Randolph | — | 84°F | 86°F (Jul) | 60°F (Oct) |
| Nashville City Lake | Washington | — | 84°F | 85°F (Jul) | 60°F (Oct) |
| Mermet Lake | Massac | — | 83°F | 83°F (Jun) | 62°F (Apr) |
| Lake of Egypt | Williamson | — | 82°F | 85°F (Aug) | 60°F (Apr) |
| Governor Bond Lake | Bond | — | 82°F | 86°F (Jul) | 55°F (Oct) |
| Fairfield Lake | Wayne | — | 82°F | 86°F (Jul) | 59°F (Nov) |
| Highland Silver Lake | Madison | — | 82°F | 85°F (Jul) | 63°F (Apr) |
| Salem Lake | Marion | — | 81°F | 82°F (Jul) | 58°F (Oct) |
| Charleston Side Channel Lake | Coles | — | 81°F | 85°F (Jul) | 61°F (Apr) |
| Wayne City Lake | Wayne | — | 81°F | 83°F (Aug) | 56°F (Nov) |
| Vermont City Lake | McDonough | — | 81°F | 85°F (Jul) | 56°F (Apr) |
| Raccoon Lake | Marion | — | 81°F | 85°F (Jul) | 54°F (Nov) |
| Horsetail Lake | Cook | 68°F | 81°F | 84°F (Jul) | 58°F (Oct) |
| Paradise Lake | Pike | — | 81°F | 87°F (Jul) | 53°F (Apr) |
| Paradise Lake | Coles | — | 80°F | 82°F (Jul) | 60°F (Apr) |
| Olney East Fork Lake | Richland | 77°F | 80°F | 84°F (Jul) | 61°F (Oct) |
| Tecumseh Lake | Hardin | — | 80°F | 82°F (Jul) | 60°F (Apr) |
| Forbes Lake | Marion | — | 80°F | 82°F (Aug) | 62°F (May) |
| Glenn Shoals Lake | Montgomery | — | 80°F | 85°F (Jul) | 57°F (Nov) |
| Saganashkee Slough Lake | Cook | 71°F | 80°F | 83°F (Jul) | 55°F (Oct) |
| Centralia Lake | Marion | 73°F | 79°F | 82°F (Jul) | 63°F (Apr) |
| Holiday Shores Lake | Madison | 78°F | 79°F | 80°F (Aug) | 51°F (Nov) |
| Tampier Lake | Cook | 65°F | 79°F | 81°F (Aug) | 52°F (Apr) |
| Lou Yaeger Lake | Montgomery | 70°F | 79°F | 84°F (Jul) | 59°F (Oct) |
| Mauvaise Terre Lake | Morgan | — | 79°F | 84°F (Jul) | 57°F (Apr) |
| Midlothian Lake | Cook | 75°F | 79°F | 81°F (Jul) | 59°F (May) |
| Powderhorn Lake | Cook | — | 78°F | 83°F (Aug) | 61°F (May) |
| One Horse Gap Lake | Pope | — | 78°F | 79°F (Aug) | 56°F (Nov) |
| Canton Lake | Fulton | — | 78°F | 82°F (Aug) | 62°F (Oct) |
| Wampum Lake | Cook | 68°F | 78°F | 81°F (Aug) | 59°F (Oct) |
| Greenfield Lake | Greene | 78°F | 78°F | 83°F (Jul) | 54°F (Apr) |
| Silver Lake | McHenry | 68°F | 78°F | 81°F (Jul) | 55°F (Oct) |
| Petite Lake | Lake | — | 78°F | 81°F (Jul) | 57°F (Oct) |
| Mattoon Lake | Cumberland | — | 78°F | 82°F (Jul) | 59°F (Apr) |
| Skokie Lagoons Lake | Cook | 65°F | 78°F | 81°F (Jul) | 55°F (May) |
| Flatfoot Lake | Cook | 78°F | 78°F | 81°F (Jul) | 60°F (Oct) |
| Bullfrog Lake | Cook | 66°F | 78°F | 81°F (Aug) | 60°F (Oct) |
| Jackson Park West Lagoon Lake | Cook | — | 78°F | 78°F (Jun) | 55°F (Oct) |
| Jackson Park East Lagoon Lake | Cook | — | 78°F | 78°F (Jun) | 56°F (Oct) |
| Kinmundy New Lake | Marion | — | 77°F | 79°F (Aug) | 60°F (Apr) |
| Vienna Correctional Center Lake | Johnson | 78°F | 77°F | 79°F (Aug) | 48°F (Dec) |
| Baumann Park Lake | Winnebago | — | 77°F | 80°F (Aug) | 58°F (May) |
| Marie Lake | Lake | — | 77°F | 81°F (Jul) | 58°F (Oct) |
| Borah Lake | Richland | — | 77°F | 79°F (Aug) | 55°F (Apr) |
| Nippersink Lake | Lake | — | 77°F | 80°F (Jul) | 56°F (Oct) |
| Lake Opeka | Cook | 72°F | 77°F | 79°F (Jul) | 58°F (Oct) |
| Sag Quarry West Lake | Cook | — | 77°F | 77°F (Jun) | 54°F (Oct) |
| Pounds Hollow Lake | Gallatin | — | 76°F | 77°F (Jul) | 57°F (Nov) |
| Vandalia Lake | Fayette | — | 76°F | 78°F (Aug) | 53°F (Nov) |
| Long Lake | Lake | 74°F | 76°F | 80°F (Jul) | 38°F (Feb) |
| Lake Springfield | Sangamon | — | 76°F | 80°F (Jul) | 55°F (Apr) |
| Bull Frog Lake | Cook | 65°F | 76°F | 79°F (Aug) | 60°F (Oct) |
| Sherman Park Lagoon Lake | Cook | — | 76°F | 78°F (Jun) | 57°F (Oct) |
| Monee Lake | Will | — | 75°F | 77°F (Jul) | 59°F (Oct) |
| Glendale Lake | Pope | 75°F | 75°F | 77°F (Aug) | 54°F (Nov) |
| Otter Lake | Macoupin | — | 75°F | 76°F (Jul) | 57°F (Nov) |
| Marquette Park Lagoon Lake | Cook | — | 75°F | 77°F (Jun) | 56°F (Oct) |
| Bluff Lake | Lake | — | 74°F | 79°F (Jul) | 57°F (May) |
| Busse Lake Main Pool | Cook | — | 74°F | 75°F (Jul) | 62°F (May) |
| Kinmundy Old Lake | Marion | — | 74°F | 76°F (Aug) | 57°F (Apr) |
| Arrowhead Lake | Cook | 77°F | 74°F | 78°F (Jul) | 56°F (May) |
| Turtlehead Lake | Cook | 74°F | 74°F | 76°F (Aug) | 61°F (May) |
| Shabbona Lake | DeKalb | — | 73°F | 75°F (Jul) | 59°F (May) |
| Channel Lake | Lake | — | 73°F | 77°F (Jul) | 57°F (May) |
| Palmyra-Modesto Lake | Macoupin | 71°F | 73°F | 75°F (Aug) | 52°F (Apr) |
| Dutchman Lake | Johnson | — | 73°F | 77°F (Jul) | 59°F (Apr) |
| Lily Lake | McHenry | — | 73°F | 76°F (Aug) | 58°F (Oct) |
| Grays Lake | Lake | — | 73°F | 80°F (Jul) | 64°F (May) |
| Round Lake | Lake | — | 72°F | 75°F (Jul) | 59°F (May) |
| Vernor Lake | Richland | — | 72°F | 75°F (Jul) | 59°F (Oct) |
| Maple Lake | Cook | — | 72°F | 75°F (Jul) | 57°F (May) |
| Hastings Lake | Lake | — | 72°F | 76°F (Jul) | 53°F (Oct) |
| Catherine Lake | Lake | — | 71°F | 75°F (Jul) | 56°F (May) |
| Randolph Lake | Randolph | — | 71°F | 73°F (Jul) | 61°F (May) |
| Loveless Lake | Macoupin | 73°F | 70°F | 73°F (Sep) | 58°F (Apr) |
| Sara Lake | Effingham | 68°F | 70°F | 72°F (Aug) | 56°F (Apr) |
| Sparta Northwest Lake | Randolph | — | 69°F | 72°F (Aug) | 54°F (Apr) |
| Axehead Lake | Cook | 72°F | 69°F | 73°F (Aug) | 51°F (May) |
| Woods Creek Lake | McHenry | — | 69°F | 71°F (Jul) | 57°F (May) |
| Sag Quarry East Lake | Cook | — | 69°F | 71°F (Jun) | 53°F (Oct) |
| Poss Lake | DuPage | 70°F | 69°F | 73°F (Jul) | 58°F (May) |
| Jackson Park Outer Harbor Lake | Cook | — | 69°F | 77°F (Jul) | 58°F (Oct) |
| Kinkaid Lake | Jackson | 70°F | 68°F | 70°F (Sep) | 61°F (May) |
| Boulder South Lake | Perry | — | 67°F | 69°F (Jul) | 56°F (Apr) |
| Diversey Harbor Lake | Cook | 73°F | 67°F | 73°F (Sep) | 56°F (Nov) |
| George Lake | Rock Island | — | 62°F | 63°F (Aug) | 54°F (May) |
| Wesslyn Cut Lake | Perry | — | 61°F | 62°F (Jul) | 53°F (Apr) |
| Big Rock Lake | Kane | — | 57°F | 58°F (Aug) | 51°F (May) |
More Illinois lake data
Frequently asked questions
Which Illinois lake has the warmest water?
Of the 90 Illinois lakes with a temperature record, Slm Side Channel Lake in St. Clair County runs warmest, averaging about 86°F at the surface in summer. Colder lakes like Big Rock Lake sit closer to 57°F.
What is a typical September water temperature in Illinois?
Across the Illinois lakes we track, typical September surface temperature averages about 72°F. That is a climatological value from EPA field readings, not the temperature right now. Summer averages about 76°F.
Where does this Illinois water temperature data come from?
Each temperature 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. 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 published through the EPA Water Quality Portal. They tell you what to expect, not the temperature right now.