Float depth is the depth from the float to the hook. Depending on the type of fishing that is being done, the float depth may vary. When targeting species such as carp and other coarse fish that inhabit the bottom of a lake, the float depth needs to be as deep as the depth of the lake where you are fishing. When targeting salmon in rivers, the float depth is usually one or two feet less than the river depth. This is done to avoid foul hooking staging salmon and snagging on the bottom.