lots of triathletes out swimming at Rickenbacker causeway that time on Saturday AM. Go E on Causeway, right after you cross the big bridge about 1 mile in, pull over into the parking lot on the right. Park, head out and swim. Should be lots of people out there. Plenty of buoys to protect you from the boat traffic.

Teamhammerheads.com
We swim at hobie beach aka tri beach in key biscayne Tues/Thurs and Saturday 7:30am 1-2miles please join us, drive on the Rickenbacker Causeway, once you go over the William Powell Bridge immediately turn right and park, see you there! Many bike and run before and after