Lake Washington — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Lake Washington, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Lake Washington today is 18.3°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 14 | 18.6°C | 22.0°C | |
| SEP 15 | 18.4°C | 22.0°C | |
| SEP 16 | 18.9°C | 22.0°C | |
| SEP 17 | 18.0°C | 22.0°C | |
| SEP 18 | 18.5°C | 22.0°C | |
| SEP 19 | 18.5°C | 22.0°C | |
| SEP 20 | 18.4°C | 22.0°C | |
| SEP 21 | 18.3°C | 22.0°C | |
| SEP 22 | 22.0°C | 18.5°C | |
| SEP 23 | 22.0°C | 18.7°C | |
| SEP 24 | 22.0°C | 18.9°C | |
| SEP 25 | 22.0°C | 19.0°C | |
| SEP 26 | 22.0°C | 19.2°C | |
| SEP 27 | 22.0°C | 19.4°C | |
| SEP 28 | 22.0°C | 19.6°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 | 3°C | 6°C | 8°C |
| March | 5°C | 8°C | 11°C |
| April | 7°C | 11°C | 15°C |
| May | 11°C | 16°C | 21°C |
| June | 13°C | 19°C | 24°C |
| July | 15°C | 24°C | 31°C |
| August | 19°C | 25°C | 30°C |
| September | 18°C | 22°C | 26°C |
| October | 12°C | 16°C | 20°C |
| November | 7°C | 11°C | 14°C |
| December | 4°C | 7°C | 9°C |
Lake Washington: Water Temperature by Location
Lake Washington: Weather Forecast
September 21
September 22
September 23
September 24
September 25
Location & Local Information
Lake Washington’s surface temperatures vary substantially through the year. In winter the lake often cools to around the low 40s °F (about 4–7 °C), while spring sees a gradual rise into the mid-40s to low 60s °F (roughly 7–16 °C). Summer brings the warmest surface conditions, commonly in the mid-60s to low 70s °F (about 18–24 °C) and occasionally reaching the mid-70s °F (around 24 °C) during heat spells. By autumn the water typically drops back into the 50s to low 60s °F range (10–16 °C). These figures are for surface layers; deeper water remains colder year-round and overall temperatures depend on weather patterns, local depth, and inflows.
Swimming in Lake Washington is allowed and takes place at many public parks and beaches, but conditions and safety vary. Municipal beaches and waterfront parks are the usual swimming locations because they are monitored for hazards and sometimes for water quality; authorities issue advisories when bacterial levels or cyanobacteria blooms make contact swimming unsafe. Other considerations include cold-water shock from cooler temperatures, boat traffic in busy channels, and submerged hazards, so swimmers often choose supervised or designated areas and pay attention to posted notices.