I LOVED Rainbow River, which is in the same area. Much better vis and the dive is a nice easy drift. Didn’t see any manatees there, though I’ve heard people say it happens.
If you want manatees, you want 3 Sisters Spring in Crystal River. We snorkeled and dove there, and there were more manatees than divers (and there were A LOT of divers!) It was very challenging to not touch them, as they are super friendly creatures and love to look at us!