Well since I spend about half my life in or around water I will say it's not the depth of the water in the lake but the makeup of the bottom. Almost every dock I've been on or around in the last 20 years there's serious muck for a foot or so before you hit solid matter. Launch ramp another story, I've pulled tons of crap out of the water after going for a dip at a launch ramp.
To lighten it up here's a good story, GF and I are at a luanch ramp by our river house, she backs the truck down, I'm unloading the skis, for some dumb reason she shuts off the truck and laid the keys in the tray of one of the jet skis to help untether them busy launch ramp county park. Well once it was off the trailer, got some water in the tray guess where the keys went, to compound it once the jet ski was fired to back off the trailer and pull onto the beach it churned up the water. Took almost 15 minutes to find the keys, made lots of friends while tying up a launch ramp since could not move the truck(one jack hole even threathened to call the sheriffs). We've taken thousands of jet skis over the years off trailers and never ever had this happen, keys are now on a floaty just in case but I still ask her every single time got the keys, I get the look and the you're number one salute each time I ask but we laugh at it.