Rend Lake — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Rend Lake, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Rend Lake today is 26.8°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
✅ As of today, the minimum water temperature ranges from 79°F (26°C) to 82°F (28°C). This is very warm water, allowing for extended stays without any discomfort. Swimming in these conditions will be particularly enjoyable, making it the ideal temperature range for those who want to relax in the sea. Additionally, water in this temperature range is suitable for children and elderly people, as it is comfortable for prolonged stays. It is important to note that these swimming tips and recommendations apply only in good weather. When the air temperature is below 68°F (20°C), and sometimes even below 77°F (25°C), swimming can be unpleasant even with relatively high water temperatures.
Water Temperature Chart Over the Last 30 Days
Table of Daily Sea Temperature Data
| Date | Current | Average | Forecast |
|---|---|---|---|
| JUL 3 | 26.5°C | 26.7°C | |
| JUL 4 | 26.9°C | 26.7°C | |
| JUL 5 | 28.7°C | 26.7°C | |
| JUL 6 | 27.6°C | 26.7°C | |
| JUL 7 | 27.5°C | 26.7°C | |
| JUL 8 | 27.3°C | 26.7°C | |
| JUL 9 | 27.3°C | 26.7°C | |
| JUL 10 | 27.3°C | 26.7°C | |
| JUL 11 | 26.7°C | 26.8°C | |
| JUL 12 | 26.7°C | 26.8°C | |
| JUL 13 | 26.7°C | 26.8°C | |
| JUL 14 | 26.7°C | 26.8°C | |
| JUL 15 | 26.7°C | 26.8°C | |
| JUL 16 | 26.7°C | 26.8°C | |
| JUL 17 | 26.7°C | 26.8°C |
* Current - Actual water temperature value
** Average - Average water temperature on this day in recent years
*** Forecast - Our water temperature forecast
Actual nearshore water temperatures may fluctuate by several degrees from the reported values, especially following heavy rainfall or extended periods of strong winds. Certain wind patterns can cause colder, deeper waters to rise and replace the sun-warmed surface water, leading to noticeable variations.
Our forecast is based on a proprietary mathematical model that considers real-time water temperature changes, historical trends, key weather patterns, wind strength and direction, and air temperature specific to each region. Additionally, we incorporate data from other resorts to enhance accuracy.
Monthly Water Temperature Range (Min, Max & Average)
| Month | Min | Avg | Max |
|---|---|---|---|
| January | 0°C | 3°C | 7°C |
| February | 1°C | 4°C | 6°C |
| March | 2°C | 8°C | 13°C |
| April | 10°C | 15°C | 20°C |
| May | 14°C | 18°C | 23°C |
| June | 20°C | 24°C | 27°C |
| July | 24°C | 27°C | 29°C |
| August | 21°C | 24°C | 27°C |
| September | 23°C | 26°C | 28°C |
| October | 16°C | 21°C | 25°C |
| November | 7°C | 12°C | 16°C |
| December | 3°C | 6°C | 9°C |
Rend Lake: Water Temperature by Location
Rend Lake: Weather Forecast
July 11
July 12
July 13
July 14
July 15
Location & Local Information
Rend Lake, a large reservoir in southern Illinois, experiences a wide seasonal range in surface water temperatures. In winter the surface often cools to roughly 35–45°F (2–7°C). During spring temperatures typically climb through the 45–65°F (7–18°C) range as air temperatures warm and stratification begins. Summer brings the warmest surface readings, commonly around 70–85°F (21–29°C) in sheltered, shallow bays on sunny days, while deeper or wind‑exposed areas remain cooler. In autumn the lake usually cools back to about 55–70°F (13–21°C) before turnover. It’s important to note that deeper water stays markedly colder year‑round, so swimmers can encounter sudden temperature drops just below the surface.
Swimming is allowed at Rend Lake in designated recreation areas and beaches managed by the U.S. Army Corps of Engineers and local authorities, because the reservoir is intended for multiple recreational uses including bathing. Access and conditions vary by site and season; some beaches may not have lifeguards and will close or post advisories during hazardous weather, blue‑green algae events, or poor water quality. For safety, swimmers should choose marked areas, be aware of boat traffic and sudden depth changes, and consider the risk of cold water or hypothermia outside the warmest months.