Lower Saint Mary Lake — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Lower Saint Mary Lake, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Lower Saint Mary Lake today is 12.3°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
⚠️ As of today, the minimum water temperature ranges from 54°F (12°C) to 60°F (15°C). The water is significantly warmer, and swimming becomes possible for most people. However, caution may still be required for prolonged stays in the water, as extended exposure can cause discomfort. This is a suitable temperature range for short swims and for those accustomed to cooler water. For more comfortable swimming, it is recommended to use proper gear. 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 |
|---|---|---|---|
| SEP 14 | 14.4°C | 17.0°C | |
| SEP 15 | 14.3°C | 17.0°C | |
| SEP 16 | 13.8°C | 17.0°C | |
| SEP 17 | 12.7°C | 17.0°C | |
| SEP 18 | 11.0°C | 17.0°C | |
| SEP 19 | 11.8°C | 17.0°C | |
| SEP 20 | 12.3°C | 17.0°C | |
| SEP 21 | 12.3°C | 17.0°C | |
| SEP 22 | 17.0°C | 12.5°C | |
| SEP 23 | 17.0°C | 12.8°C | |
| SEP 24 | 17.0°C | 13.0°C | |
| SEP 25 | 17.0°C | 13.2°C | |
| SEP 26 | 17.0°C | 13.5°C | |
| SEP 27 | 17.0°C | 13.7°C | |
| SEP 28 | 17.0°C | 13.9°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 | 1°C | 4°C |
| February | 0°C | 3°C | 5°C |
| March | 0°C | 3°C | 6°C |
| April | 1°C | 4°C | 6°C |
| May | 3°C | 8°C | 13°C |
| June | 9°C | 14°C | 18°C |
| July | 12°C | 17°C | 21°C |
| August | 17°C | 21°C | 25°C |
| September | 14°C | 17°C | 20°C |
| October | 5°C | 10°C | 15°C |
| November | 1°C | 5°C | 9°C |
| December | 0°C | 2°C | 5°C |
Lower Saint Mary Lake: Water Temperature by Location
Lower Saint Mary Lake: Weather Forecast
September 21
September 22
September 23
September 24
September 25
September 26
Location & Local Information
Lower St. Mary Lake, sitting at high elevation in northern Montana, typically has cold water year-round. In spring and early summer the surface temperatures commonly range from about 35–50°F (2–10°C) as snowmelt feeds the lake. Peak summer surface readings in July and August can warm into the neighborhood of 50–60°F (10–16°C) in shallow, sun-exposed areas, but deeper or shaded parts remain colder. By early fall the lake cools back to roughly 35–45°F (2–7°C), and in winter the lake is often ice-covered or close to freezing. These ranges vary with season, recent weather, wind, and exact location on the lake, so mid-summer warmth is usually limited and short-lived.
Swimming is generally allowed but uncommon and requires caution because the water is cold enough to cause cold-water shock and hypothermia even after a brief immersion. There are no lifeguards, services are sparse, and sudden winds or changing conditions can make exits difficult, so visitors should treat swims as brief, deliberate exposures (ideally with a wetsuit) rather than long recreational swims. For safety, people often stick to wading near shore, wear protective gear, and avoid swimming alone; these precautions explain why formal swimming activity at Lower St. Mary Lake is limited despite being permitted.