
Well, what’s warm enough for you and what’s warm enough for me might be two different things – I’m a big wimp! In general 70 degrees Fahrenheit is warm enough that you’ll start seeing people in the water, and at 75 degrees, most people will enjoy swimming. At 80, even I’ll stay in for hours!
You will usually be able to swim (without freezing off your flip-flops) at most Florida beaches between April and October. Obviously, the farther south you go, the warmer the water will be. The Gulf of Mexico is generally a few degrees warmer than the Atlantic. Keep in mind water temps don’t vary hugely from day to day like air temperatures can.
If you want a more exact idea of what to expect, check out these charts of average water temperatures for the Gulf of Mexico and the Atlantic Ocean from the National Oceanographic Data Center’s website.