I actually work for Citrus County (where Crystal River is). There is a place in Crystal River to dive - King`s Bay. It`s roughly 35 - 40ft with a cavern/room. There is an Encore campground on Fort Island Trail (this is a road that leads out to the Gulf of Mexico and to a boat ramp on Crystal River). It`s a very nice campground. Chassahowitzka River Campground is another decent campground. I know you were asking about the East coast and the only Spring I`m aware of is Blue Springs State Park. The problem is that when the manatees are in the spring (which they are now!) you cannot go into the water.