WE used to go scalloping north of the Barge canal in the grass flats..
They are fairly shallow. I am five foot three and found the water chest deep. My dad pushed me overboard more than a few times.. he thought it was funny.
I would suggest a dingy or flats boat with outboard.
Previous poster is correct about depths in Crystal River, my hometown.
However be very careful going up the river and keep a good lookout for manatees..they are everywhere and can trash a prop in a heartbeat.
The island at the beginning of the river, just inside used to be a great stopping of point.
Weekends in the summer can be a real PIA, with the powerboats going flat out up the river to the Gulf. I strongly suggest mid week if you crave peace and quiet.
Lots of gators in the swamp just west of the Indian mound.
Winter river depths can be shallow, stay IN the channel.