Decatur — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Decatur, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Decatur today is 29.9°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
✅ As of today, the minimum water temperature is above 82°F (28°C). This is very warm water, which may feel almost hot to most people. Swimming in such conditions is perfect for those seeking relaxation and comfort in the water. These waters are often preferred for relaxation in hot weather, as the water temperature does not cool the body significantly. However, it is important to remember that in such warm waters, caution is necessary, as prolonged exposure without rest can lead to overheating. 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 14 | 26.7°C | 26.0°C | |
| JUL 15 | 29.2°C | 26.0°C | |
| JUL 16 | 29.4°C | 26.0°C | |
| JUL 17 | 29.6°C | 26.0°C | |
| JUL 18 | 30.2°C | 26.0°C | |
| JUL 19 | 30.2°C | 26.0°C | |
| JUL 20 | 30.4°C | 26.0°C | |
| JUL 21 | 30.2°C | 26.0°C | |
| JUL 22 | 26.0°C | 29.7°C | |
| JUL 23 | 26.0°C | 29.5°C | |
| JUL 24 | 26.0°C | 29.3°C | |
| JUL 25 | 26.0°C | 29.1°C | |
| JUL 26 | 26.0°C | 28.9°C | |
| JUL 27 | 26.0°C | 28.7°C | |
| JUL 28 | 26.0°C | 28.5°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 | 2°C | 5°C |
| February | 0°C | 3°C | 7°C |
| March | 0°C | 6°C | 12°C |
| April | 8°C | 13°C | 19°C |
| May | 14°C | 18°C | 22°C |
| June | 20°C | 23°C | 26°C |
| July | 21°C | 26°C | 31°C |
| August | 23°C | 26°C | 29°C |
| September | 21°C | 24°C | 27°C |
| October | 13°C | 17°C | 21°C |
| November | 5°C | 10°C | 14°C |
| December | 0°C | 3°C | 6°C |
Decatur: Weather Forecast
July 22
July 23
July 24
July 25
July 26
Location & Local Information
Decatur, located in central Illinois, lies along the Sangamon River and is home to Lake Decatur, a large reservoir created for both recreation and water supply. The region’s continental climate brings cold winters and warm summers, leading to wide seasonal variations in water temperature. During winter, the surface temperature in Lake Decatur and nearby rivers often ranges from 0–3 °C (32–37 °F), and smaller sections can freeze. In spring, as the ice melts and air temperatures rise, the water warms to about 8–15 °C (46–59 °F). By midsummer, the surface water typically reaches 22–26 °C (72–79 °F), while deeper areas remain several degrees cooler. In autumn, temperatures drop again to around 10–16 °C (50–61 °F) before returning to near freezing in late fall.
Swimming in Decatur is officially allowed at designated areas, particularly around Lake Decatur, which is a central point for summer recreation. The best time for swimming is from late June through early September, when water temperatures are comfortably warm and weather conditions are stable. The lake’s wide shoreline and maintained parks make it accessible for swimming, boating, and fishing. Outside the summer season, colder temperatures make swimming impractical, though the lake remains popular for scenic walks, wildlife observation, and other outdoor activities.