When you think of diving, you think of a harpoon!
But there is no harpoon...
I would say, make a harpoon wich you can use by scuba diving but also out of water, it wont be the best weapon out of the water, but just that you have 'something' to shoot with, wich you can easily use underwater, and out of the water.

'add a harpoon to the scuba diving' {F17605}