I don't get it, how would the "cycle" in the ocean be separate from the one on land? Fairly certain it doesn't work that way. Sure there may be monsters in that world changing some stuff, but this is probably not one of them (if anything, considering they eat fish, wouldn't her ideal end up starving the ocean?). Either way, I suspect anything done on land will eventually find its way to the ocean anyway. Though maybe not? Again, monsters, so maybe her way does not conserve matter and depletes the planet slowly?
Though I get that she who probably swims a lot is not appreciative of him relieving himself so near the same spot she plays. Should at least do it far away.