CWTG - NCEI Coastal Water Temperature Guide - Frequently Asked Questions

Frequently Asked Questions

1. What is the best water temperature for swimming in the ocean?: There's no real optimal temperature. It's more of a question of preference. A little cooler than your body temperature (98.6° Fahrenheit) should not be too cold so that you don't get chilled. 70° to 78° Fahrenheit is the range where most folks feel "comfortable" swimming.
2. What happens in cold water?: Hypothermia, a subnormal body temperature, can occur in waters with cold or even moderate temperatures. Even in the summer, prolonged immersion in water temperatures below 70° Fahrenheit can produce hypothermia. The body quickly surrenders its heat to cold water and chilled blood can impair the heart and brain. Swimming or treading water will greatly increase heat loss and may limit your range to less than one-half mile. Use H.E.L.P. (Heat Escape Lessening Posture) if alone or huddle with others. This will significantly extend your survival time.
3. Can water temperatures differ between near-shore and offshore sites at the same latitude?: Yes, several factors can influence the sea surface temperatures along near shore waters more so than offshore waters. These factors include river runoff, higher cooling and heating rates, continental air masses, near-shore ocean currents, and upwelling effects.