Tomhannock Reservoir — Current Water Temperature, Annual Trends and Forecast
This page provides information on the current water temperature in Tomhannock Reservoir, trends, monthly ranges and the forecast for the coming days.
Current Water Temperature
Water Temperature in Tomhannock Reservoir today is 20.2°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 |
|---|---|---|---|
| SEP 14 | 20.9°C | 20.5°C | |
| SEP 15 | 20.9°C | 20.5°C | |
| SEP 16 | 21.3°C | 20.5°C | |
| SEP 17 | 20.4°C | 20.5°C | |
| SEP 18 | 19.4°C | 20.5°C | |
| SEP 19 | 20.1°C | 20.5°C | |
| SEP 20 | 21.2°C | 20.5°C | |
| SEP 22 | 20.5°C | 20.2°C | |
| SEP 23 | 20.5°C | 20.2°C | |
| SEP 24 | 20.5°C | 20.2°C | |
| SEP 25 | 20.5°C | 20.3°C | |
| SEP 26 | 20.5°C | 20.3°C | |
| SEP 27 | 20.5°C | 20.3°C | |
| SEP 28 | 20.5°C | 20.3°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 | 2°C | 4°C |
| February | 0°C | 2°C | 5°C |
| March | 1°C | 3°C | 6°C |
| April | 2°C | 8°C | 14°C |
| May | 11°C | 14°C | 18°C |
| June | 14°C | 18°C | 23°C |
| July | 20°C | 25°C | 29°C |
| August | 20°C | 23°C | 27°C |
| September | 17°C | 21°C | 24°C |
| October | 11°C | 14°C | 17°C |
| November | 6°C | 10°C | 13°C |
| December | 0°C | 4°C | 7°C |
Tomhannock Reservoir: Water Temperature by Location
Tomhannock Reservoir: Weather Forecast
September 21
September 22
September 23
September 24
September 25
Location & Local Information
Tomhannock Reservoir’s surface water temperatures vary with season and depth. In winter the surface commonly hovers near freezing, roughly 32–39°F (0–4°C). Spring warming pushes surface values into the 40s and low 50s°F (4–12°C) as ice melts and stratification begins. By summer, surface temperatures typically reach the mid‑60s to mid‑70s°F (18–24°C) on warm days, though shallow bays can get slightly warmer and deeper water remains much cooler. In autumn the lake cools back through the 50s and 40s°F (10–10°C to 4–12°C) as turnover occurs. Because Tomhannock is a large, relatively deep reservoir, thermal stratification means sub‑surface temperatures can be substantially colder than surface measurements, posing a hypothermia risk for sudden immersion even in summer.
Swimming in Tomhannock Reservoir is generally not permitted. The reservoir serves as a municipal drinking water supply, and regulations and signs around the property typically prohibit bathing or wading to reduce contamination risk and protect water quality. Beyond water‑supply protections, safety concerns such as cold deep water, limited visibility, and boat traffic are additional reasons for restrictions. Visitors should observe posted rules and use designated recreation areas nearby where swimming is allowed and monitored.