Guernsey Reservoir — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Guernsey Reservoir, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Guernsey Reservoir today is 19.4°C.
Water Temperature: Daily Trends, Historical Records, and Forecast
⚠️ As of today, the minimum water temperature ranges from 65°F (18°C) to 68°F (20°C). This is already quite warm water, which is ideal for most people. Swimming becomes comfortable, and prolonged stays in the water do not cause discomfort. This temperature is perfect for family trips and for those who prefer warmer water. It is also comfortable for water sports such as surfing or swimming. 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 13 | 21.4°C | 21.4°C | |
| SEP 14 | 21.4°C | 21.4°C | |
| SEP 15 | 19.6°C | 21.4°C | |
| SEP 16 | 20.6°C | 21.4°C | |
| SEP 17 | 20.0°C | 21.4°C | |
| SEP 18 | 20.6°C | 21.4°C | |
| SEP 19 | 19.5°C | 21.4°C | |
| SEP 20 | 19.9°C | 21.4°C | |
| SEP 21 | 21.4°C | 19.5°C | |
| SEP 22 | 21.4°C | 19.6°C | |
| SEP 23 | 21.4°C | 19.7°C | |
| SEP 24 | 21.4°C | 19.8°C | |
| SEP 25 | 21.4°C | 19.9°C | |
| SEP 26 | 21.4°C | 20.0°C | |
| SEP 27 | 21.4°C | 20.1°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 | 0°C | 3°C | 6°C |
| March | 0°C | 6°C | 12°C |
| April | 4°C | 9°C | 15°C |
| May | 8°C | 14°C | 21°C |
| June | 15°C | 19°C | 23°C |
| July | 21°C | 25°C | 30°C |
| August | 21°C | 25°C | 30°C |
| September | 17°C | 21°C | 26°C |
| October | 9°C | 14°C | 19°C |
| November | 6°C | 11°C | 14°C |
| December | 3°C | 5°C | 7°C |
Guernsey Reservoir: Water Temperature by Location
Guernsey Reservoir: Weather Forecast
September 22
September 23
September 24
September 25
September 26
Location & Local Information
Guernsey Reservoir, located in eastern Wyoming, experiences a wide range of water temperatures through the year because of its elevation and seasonal climate. In spring (April–May) surface temperatures commonly sit between about 35–55°F (2–13°C) as snowmelt and cool inflows moderate the water. Peak summer surface temperatures (June–August) typically warm to roughly 60–75°F (15–24°C) in shallower bays on warm years, though deeper water remains noticeably cooler. In early fall (September–October) temperatures usually fall into the 45–65°F (7–18°C) band as air temperatures drop, and in winter the reservoir can approach freezing, about 32–40°F (0–4°C), with ice possible in sustained cold spells. Local conditions, depth, and wind exposure produce significant variation across the reservoir.
Swimming is generally permitted at Guernsey Reservoir because the site is managed for multiple recreational uses including boating, fishing, and shore recreation; designated park areas typically accommodate swimming. That said, there are no routine lifeguards, and access can be limited or discouraged near the dam, boat ramps, and in high-traffic boating zones. Cold water, sudden depth changes, submerged hazards, and boat traffic create real safety risks—especially early and late season when temperatures are low—so swimmers should follow posted signs, use flotation as appropriate, and exercise caution.