Biting flies attracted by water on winter cover

[Poconos]

Standing water can be a breeding ground for a bunch of critters. I have no idea what to do other than flush it off once in a while but one idea that comes to mind is adding something to the water to either kill or discourage them. I have NO IDEA if cover damage can occur but what about a few drops of oil that will form a thin molecular film or maybe borax or baking soda. Maybe RV antifreeze or the older green stuff ethelyne glycol. Just some crazy ideas and I'd like to hear comments too.
Al

[waste]

Nicole, not sure how it would impact the cover but last year we had 3 sets of fiberglass steps full of water and mosquitos ay our shop - I finally got tired of the squtos and crushed a trichlor tab and put a few small peices in each step - the mosquitos went away. I think the cya helped keep the bugs away for ~ 2 mos (which was how long I waited to repeat the proceedure).
Don't know how practical this would be for you (nor the effect on your cover - if the cover would be damaged by the low pH or concentrated cl, it's not worth it), but thought I'd at least toss it out as an idea. BTW, we are talking about a relatively small amt of water, so whatever you use, you shouldn't need much, and it only has to last a month before the cold gets 'em.