Lake Saint John — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Lake Saint John, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Lake Saint John today is 11.7°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
❌ As of today, the minimum water temperature ranges from 50°F (10°C) to 54°F (12°C). The water is slightly warmer, but still cool for most people. Swimming in such conditions is possible, but for most people, the time spent in the water should be limited to avoid hypothermia. Even experienced swimmers may feel discomfort if they stay in the water for too long. To improve comfort and safety, a wetsuit can be used. 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 |
|---|---|---|---|
| OCT 5 | 13.4°C | 12.0°C | |
| OCT 6 | 13.2°C | 12.0°C | |
| OCT 7 | 12.3°C | 12.0°C | |
| OCT 8 | 12.3°C | 12.0°C | |
| OCT 9 | 12.3°C | 12.0°C | |
| OCT 10 | 12.1°C | 12.0°C | |
| OCT 11 | 11.2°C | 12.0°C | |
| OCT 12 | 11.6°C | 12.0°C | |
| OCT 13 | 12.0°C | 11.7°C | |
| OCT 14 | 12.0°C | 11.7°C | |
| OCT 15 | 12.0°C | 11.7°C | |
| OCT 16 | 12.0°C | 11.8°C | |
| OCT 17 | 12.0°C | 11.8°C | |
| OCT 18 | 12.0°C | 11.8°C | |
| OCT 19 | 12.0°C | 11.8°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 | 7°C | 12°C |
| February | 0°C | 8°C | 15°C |
| March | 0°C | 9°C | 17°C |
| April | 2°C | 11°C | 20°C |
| May | 8°C | 15°C | 23°C |
| June | 15°C | 20°C | 24°C |
| July | 17°C | 23°C | 29°C |
| August | 19°C | 25°C | 29°C |
| September | 17°C | 21°C | 25°C |
| October | 5°C | 12°C | 19°C |
| November | 3°C | 7°C | 10°C |
| December | 0°C | 5°C | 8°C |
Lake Saint John: Water Temperature by Location
Lake Saint John: Weather Forecast
October 13
October 14
October 15
October 16
October 17
Location & Local Information
Lake Saint John in northeastern South Dakota typically shows a clear seasonal pattern in surface temperatures. During late winter and early spring the water often hovers near freezing, roughly 35–45°F (2–7°C). As air temperatures warm in late spring and early summer, surface readings commonly rise into the mid-50s to upper-60s °F (13–20°C). Peak summer warmth usually brings the warmest swimming conditions, with surface temperatures frequently in the 70–80°F range (21–27°C) on sunny days; shallow bays and sheltered areas can warm a few degrees higher. In autumn the lake cools again toward springlike values, and by winter lakes in this region often develop ice cover that keeps temperatures at or just above freezing.
Swimming at Lake Saint John is generally possible where public access points and beaches are provided, and many visitors swim in the warmest months when surface temperatures are most comfortable. However, suitability depends on local conditions: water quality advisories, aquatic vegetation, or cyanobacteria blooms can temporarily restrict swimming, and cold or icy conditions in shoulder seasons and winter make swimming unsafe. Visitors should follow posted signs, observe water clarity and weather, and use usual safety precautions such as life jackets and swimming with a companion.