I've got loads of stale water in 4 ponds from 150G down to 20G. I let those go wild and they filled with tadpoles eating the mosquito larvae and the water attracts dragonflies, the deadliest hunters on Earth. Part I didn't expect, they went "natural" in 2 weeks! I think much of that was throwing native water plants with their mud balls I dug out.

For water you can't control like that, say a birdbath, a lemming turned me onto Mosquito Dunk. Take a 1/4 piece and throw it in. Makes bacteria that kills the larvae. I set buckets of swamp water around my camp for traps, hit them and the 2 birdbaths with dunk once a month. Seemed to work, but I need to try again next year.