I have seen shellcracker beds in a clear, deep, spring fed "river" . I think the beds were in water about 16 to 20 ft deep. Most of the time I would catch them in 2 to 5 foot water where the river dumped into the lake. I have gigged or bow shot tilapia in less than 1 ft of water up to 16ft deep when I had a 20 gig pole. Those do not look like the tilapia beds I normally see in central florida..Drop a bait down and see what bites.