Digging a bog pond is fun
Eeek ! non-native, and actually invasive fish, will bring the ranters back to this post, reeally fast.
Bettas as invasives:
'Damn'busia - Gambusia> mosquito fish as invasives:
The mosquito dunk: It's pre-emergent'donuts', [not real ones], or granules, that contain Bt, a targeted bacteria, that kills [mostly] mosquitos. There may be a problem with this, now too, errg. [bees, butterflies]
Before you do anything else, check with your local, state or county, agricultural extention service. They have the best and latest, advice for your area. They should be able to recommend your best options.