Is there an all-natural additive that can prevent mosquitoes from breeding in still water?

I’m wondering if there’s something I can add to a pond, or a small pool, or some kind standing water in my backyard that is all-natural and, most importantly, non toxic and totally safe for dogs. I’ve got a couple of dogs that love water and get hot in the summer, but I don’t want to create more mosquito havens in my backyard…