The Homosassa River is premium manatee viewing with the Crystal River being the second choice. I spent 3 nights in Crystal River so I booked manatee snorkel tours with 2 different companies - both excellent.
The reputable manatee tour companies do not allow you to swim after the manatees - they must approach you and you cannot swim after them. The first snorkel trip was on the Crystal River at 8:00am. We saw 2 manatees; one of which stayed with us and allowed us to pet and scratch him. The second snorkel trip was at 7:00am at the Homosassa River near one of the manatee sanctuaries where we saw many manatees and several came around us and allowed us to pet them. You can only snorkel with them - SCUBA has been outlawed as the bubbles frighten them away. I was very impressed with both companies in the way they found the manatees so quickly and were very careful to prevent anyone from harassing the manatees when we were in the water with them. The water was 72-degrees and you do need a wetsuit which can be rented at the tour company.
Equipment: You need a snorkel and mask and fins and wet suit - all gear can be rented at the tour company.
I did a sunset pontoon boat tour on the Homosassa River. It was a nice relaxing way to end the day.
Another day I did the airboat ride to the Gulf of Mexico where we saw many birds.
Equipment: Jacket or windbreaker and camera