>> reporter: it is among the world's best trout streams. and on any other weekend in july this river might be overrun by fishermen. but montana's yellowstone river is flanked by nearly 200 cleanup workers. >> we understand this is a very serious event. we understand that we need to get our full arms around where the exposure areas are. >> reporter: an estimated 42,000 gallons gushed into the river this weekend. an early theory is that powerful waters flooding this community and running at four times the normal rate may have damaged the pipeline, which was shut down within six minutes of a huge flux in pressure readings. >> when you build a pipeline through a river you expect floods. a river like yellowstone floods all the time. we can't expect our pipelines to break every time a flood happens. >> reporter: local photographers have captured images of birds sitting in oil. but officials say they have no widespread reports of damaged wildlife. exxonmobil believes the oil has been contained to a 15-mile stretch.h. but after early criticism from montana's governor, officials