United States — Water Temperature in Seas, Lakes and Rivers

Sea Water Temperature Along the Coast

Places with the Warmest Sea Water Today

The Most Popular Seaside Places

Coastal Seas and Oceans

Water Temperature in Lakes and Rivers

Popular Lakes

Popular Rivers

Popular Places

Water Temperature and Swimming Overview

Water Temperature Trends

The United States has a wide range of coastal sea temperatures driven by latitude and ocean currents. On the Atlantic coast, waters in the Northeast are cool much of the year, often near 0–10 °C (32–50 °F) in winter and rising to roughly 15–25 °C (59–77 °F) by late summer; the Southeast Atlantic tends to be milder, with winter temperatures commonly 10–22 °C (50–72 °F) and summer values around 22–28 °C (72–82 °F). The Gulf of Mexico is among the warmest U.S. coasts, frequently 18–30 °C (64–86 °F) from winter to late summer. Along the Pacific, northern California, Oregon and Washington remain cool year-round, typically 8–18 °C (46–64 °F) in summer, while southern California can reach 15–24 °C (59–75 °F) in the warm months. Seasonal variability is pronounced, with cold winters in the north and much warmer summers in southern and shallow coastal waters.

Swimming Conditions

In inland waters, the Great Lakes show strong seasonality: near-freezing to 4 °C (32–39 °F) in winter with ice in places, warming to about 12–22 °C (54–72 °F) in summer. Small, shallow lakes and some rivers can reach 20–28 °C (68–82 °F) in summer, while mountain streams remain cold from snowmelt, often 4–12 °C (39–54 °F). Swimming is commonly permitted in designated beaches, public lakes and monitored river access points during warmer months, but local rules, lifeguard availability, water quality advisories, rip currents and cold-water risks like hypothermia and cold shock determine safety. Authorities may close sites for pollution, algal blooms or hazardous conditions, so swimmers are advised to follow posted guidance and seasonal warnings.