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 21.8°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
✅ As of today, the minimum water temperature ranges from 68°F (20°C) to 74°F (23°C). The water is warm and pleasant for swimming, and in this range, one can stay in the water for extended periods without the risk of hypothermia. This is the ideal temperature for relaxation, swimming, and water sports. Families with children, as well as outdoor enthusiasts, will enjoy swimming and time spent in the water. For most people, this is the optimal temperature for a comfortable beach experience. 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 |
|---|---|---|---|
| JUN 5 | 20.7°C | 23.0°C | |
| JUN 6 | 21.0°C | 23.0°C | |
| JUN 7 | 23.3°C | 23.0°C | |
| JUN 8 | 24.5°C | 23.0°C | |
| JUN 10 | 24.7°C | 23.0°C | |
| JUN 11 | 23.9°C | 23.0°C | |
| JUN 13 | 23.0°C | 21.9°C | |
| JUN 14 | 23.0°C | 21.9°C | |
| JUN 15 | 23.0°C | 22.0°C | |
| JUN 16 | 23.0°C | 22.0°C | |
| JUN 17 | 23.0°C | 22.1°C | |
| JUN 18 | 23.0°C | 22.2°C | |
| JUN 19 | 23.0°C | 22.2°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
June 12
June 13
June 14
June 15
June 16
June 17
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.