Someone told me about beyondpesticides.org today, and also said a lot of the Ag universities are in bed with chemical companies that support Ag. I suspect in California things may be a lot different than what's done in the Carolinas, Louisiana, Texas, etc, in terms of Ag, but maybe not so much for lawn care?
Personally, I always strive for organic use and do mostly only use chicken manure, milorganite (human sludge), and neem oil. But occasionaly will use azoxystrobin (in Maxide) to prevent brown patch, rust, etc during wet seasons in the south.
Wikipedia has what seems to be a favorable ecotoxicology report for azoxystrobin which states (credit to Wikipedia):
"Azoxystrobin has a favorable ecotoxicological profile, meeting the expectations of agricultural demand.
Its toxicity is low for mammals, birds, bees, insects, and earthworms. It is highly toxic for freshwater fish and invertebraes and very highly toxic for marine invertebraes. (this is disputed. Please read discussion page for details)
Azoxystrobin is broken down into the soil. The agent is not very mobile and therefore is unlikely to penetrate further in the soil and come into contact with groundwater."
Thus, it looks like it is unlikely to reach the rivers, streams, but I think there are invertebrates all around us(?)