Points on the east and west coasts where it gets just too cold for you to swim most days of the year

[GeoffD]

I’m Massachusetts South Coast near the Rhode Island line. My beach reliably gets to 68F by June 15 and stays above that into October. We have had the remnants of a tropical storm with days of rain and big ocean surf. It’s barely at 68F now but will warm up a bit once the sun appears. There’s usually 4 months where it’s swimmable.

Massachusetts Bay north of Cape Cod has much colder water. I see 63F. That’s locally called wicked pissah cold.

[GeoffD]

Originally Posted by Tusco

Is Old Orchard Beach's water really warmer than San Diego's water during the summer? I do have yet to swim in either Maine or California myself (I only swam in VA, NJ, and HI). I knew the Atlantic's water is warmer than the Pacific's water on the same latitude.

It depends. I lived in a house with a boat dock in Portsmouth NH on the Maine line for a decade. If you get a high pressure parked over New England for a few weeks with no storms, the top layer warms up. I’ve seen 75F. 20 feet down, it’s 60F. If there’s a storm that churns everything up, it reverts to 60F.

You have to get as far south as Chatham Ma for the water to be reliably swimmable in the summer. That is beyond the currents that flow south from the Gulf of Maine.

[jcp123]

I’ve never been able to brave the Lake Ontario waters. It’s always too damn cold, and not worth it anyway since I’m always suspicious of what chemicals etc are hanging out in it.

[ejisme]

You didn't say outdoor in natural river, lake or ocean. Heated pools can be swam in year-round anywhere. You could also get one of those backyard Swim Spas that are advertised a lot. Then you could comfortably swim outside when it's below freezing in your backyard.