Lake Sammamish — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Lake Sammamish, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Lake Sammamish today is 20.6°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 |
|---|---|---|---|
| AUG 24 | 21.1°C | 25.0°C | |
| AUG 25 | 21.0°C | 25.0°C | |
| AUG 26 | 21.0°C | 25.0°C | |
| AUG 27 | 21.0°C | 25.0°C | |
| AUG 28 | 20.9°C | 25.0°C | |
| AUG 29 | 21.1°C | 25.0°C | |
| AUG 30 | 21.1°C | 25.0°C | |
| AUG 31 | 20.8°C | 25.0°C | |
| SEP 1 | 21.5°C | 20.6°C | |
| SEP 2 | 21.5°C | 20.7°C | |
| SEP 3 | 21.5°C | 20.7°C | |
| SEP 4 | 21.5°C | 20.8°C | |
| SEP 5 | 21.5°C | 20.8°C | |
| SEP 6 | 21.5°C | 20.9°C | |
| SEP 7 | 21.5°C | 20.9°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 | 4°C | 8°C |
| February | 2°C | 5°C | 8°C |
| March | 5°C | 8°C | 11°C |
| April | 6°C | 11°C | 15°C |
| May | 12°C | 17°C | 21°C |
| June | 13°C | 19°C | 24°C |
| July | 15°C | 23°C | 31°C |
| August | 20°C | 25°C | 30°C |
| September | 17°C | 22°C | 26°C |
| October | 13°C | 17°C | 20°C |
| November | 7°C | 11°C | 14°C |
| December | 4°C | 7°C | 9°C |
Lake Sammamish: Water Temperature by Location
Lake Sammamish: Weather Forecast
September 1
September 2
September 3
September 4
September 5
Location & Local Information
Lake Sammamish, near Seattle in Washington state, typically runs cool compared with more southerly swimming spots. Seasonal surface temperatures commonly fall in the approximate ranges of winter 40–50°F (4–10°C), spring 45–60°F (7–16°C), summer 60–72°F (16–22°C), and early fall 50–60°F (10–16°C). Peak summer surface readings often sit around the upper 60s to low 70s °F (about 20–22°C) on warm, calm days, while deeper water remains noticeably colder year-round. These figures vary with weather, wind, and inflows, so local measurements can differ from season averages.
Swimming in Lake Sammamish is generally permitted and popular in summer where public access and beaches exist, because temperatures during the warmest months are tolerable for many recreational swimmers. However, visitors should watch for posted health advisories or closures that may occur after heavy rain or during algal-bloom episodes, which can raise bacteria or toxin concerns. Even when allowed, cold-water shock and rapid heat loss are risks in water below the mid-60s °F (around 18°C), so swimmers should exercise caution, avoid long exposures in cooler water, and follow local safety guidance.