It's called go buy a map. the blue lines are rivers and there are bridges every time a black line crosses a blue line. If you see giant boats that means that it is deep water. Stop your car get out and take a quick swim or jump. You need 10-12 feet of water to safely make a jump. You also need a large area of this deep water so you don't hit any rocks. I use a 20 foot rope w/a wieght. i tie a knot at 12 and 14 feet and then swim in circles to check depth.