Harpoons are only available while Leon is on the motor boat located on the Lake. There is an unlimited amount and only one can be thrown at a time. Instead of aiming with a laser sight, a more traditional cross-hair appears when using them. The harpoons do not fly in a straight line; rather, they realistically arc with distance.
They are the only weapon that can be used against Del Lago. It takes about 8-12 harpoons to kill it depending on the difficulty level. It is possible to hit Del Lago with at least three spears every time it charges at Leon's boat.
Players can also use the harpoons to kill near by fish and the Colmillos to save ammunition, provided that they go back the path they originally came from.