To follow up on the thread about water quality and fish biomass in the Bow River, I thought I'd pass on this link to a real short report put out by some of the guys at the U.S.G.S. in Iowa City that I used to work with.
http://www.iowapolicyproject.com/2006docs/...-USGS-ExSum.pdf
It talks briefly about contaminants from wastewater effluent that we don't always think about. Pharmaceuticals, for example. In work following up this report on numerous outings we actually were able to find physical and chemical evidence of antidepresents and hormones in the fish. Physcially, fish like the fathead minnow that in the males generally has very strong male features were becoming more feminized. In the white sucker, we found measuravle levels of antidepresants in their brains. As you might suspect, the upstream fish were free of these effects, and at and downstream from the plant outflow they were significant.