You might be a little early to see a lot of Manatee’s. They really flock to the springs when the Gulf water gets below 72 Degrees. American Pro Diving in Crystal River does them. I’ve never used them because I have my own boat but they have been doing it a long time. They go out of both Crystal River and Homosassa. Good luck, hope you enjoy your trip.
Dan
American Pro Diving
821 SE Highway 19
Crystal River, Florida 34429
352-563-0041
800-291-DIVE