Its a birds eye view of someone fishing! The "blood" is wet wooden decking! follow the wet footsteps to the grass, and they go slightly to the right hand side of the bridge, probably to his "Keep net" that would be placed on the bank side, so not to disturb the fish he's fishing for, look closely, there is also another object near the bridge, on the grass...
Shadow of the man on the water, has the body language of someone holding a fishing rod
Thom
