I know it's a "bit" outside your search parameters, but Crystal River, FL is about 75 miles south of High Springs. In late April there will probably still be a few manatee in the Crystal River basin. It's not scuba, just snorkeling. But swimming with the manatee should be on every diver's bucket list.

I suggest Bird's Underwater as your contact if this is something that would interest you. Early morning (sunrise) is the best manatee encounters.

p.s.- full wet suit. Manatee swims can get cool FAST because you are not exercising!