The item is a Linch Pin (or alternate spelling; Linchpin, Lynch Pin, Lynchpin), rather than a hitch pin. These are used to lock in place connecting pins on various equipment. This pin goes through a hole in the end of a larger connecting pin or shaft, and the spring retainer ring snaps down to lock this in place. Farm equipment has these on many of the attachments. I've had the opportunity to use (and lose) a few of these over the years. The blue paint on this one reminds me of Ford farm equipment from a few years back, or New Holland more recently. Finding this in or near water maybe could rule out farm equipment. Since these Linch Pins are multifunctional, there are no doubt applications for possible use even in boat equipment.