[IrishCatholic]

Actually I think it sucks up oxygen. It is one of the reasons there is a dead zone in the Gulf of Mexico the size of Rhode Island. Excessive fertilizers from agricultural production causes algae blooms and depletes the oxygen in the water. On the flip side I could run all of my vehicles off the crap that is on my own lake. I can't decide if that is a good thing or a bad thing.
Oh, by the way I found that dead zone thing from the National Oceanographic Service (NOS). Just in case you thought it was greenie propaganda.

[graycamel]

Apparently they don't suck up all that much oxygen till they die, then they take so much that the fish have none left. There is much less oxygen in water than in air to begin with, and it can't be replenished fast enough. The problem is often solved in lakes around here with oxygen pumps into the water for the fish.