Our garden drainage system flows into a collector system. When it gets full, a submersible sump pump empties it. But in the mean time it can be full of pretty nasty & stagnant water. I want to put something into the water that will kill mosquitos but will not be a hazard to the environment. 'Any recommendations?

-- Macs

Mosquito Dunks can work.
http://www.dirtdoctor.com/organic/garden/store/type/23/