On Thursday night, about 20 concerned people gathered at Durango Public Library to hear one woman’s answer to an effortlessly gripping question: “Who pooped in the river?”

According to Melissa May – a natural resource specialist for San Juan Soil and Water Conservation District who analyzed microbial source tracking results for the Animas River in Colorado and New Mexico – the answer is, in short, humans pooped in it.

May based her conclusions on samples collected from sites along the Animas in 2013 and 2014 because of $300,000 worth of grant money, 68 volunteer samplers who were “basically pooper-scooping for science,” five private landowners and three laboratories.

May told the assembled audience that her first move was establishing a list of suspects: humans, cows, pigs, birds, chickens, gulls, geese, deer, dogs and horses.

She proceeded to winnow that list down by testing samples for bacteroides and E. coli, which “are natural fecal indicators that naturally inhabit warm-blooded animals and are biochemically unique to their animal hosts,” she said.

“Basically, both bacteroides and E. coli indicate that there’s poop in the water. They don’t show that there’s necessarily an immediate danger. But they are an indicator that other organisms that might cause harm could be there,” she said.

Resoundingly, test results showed that bacteria unique to human feces was in the water; by one measure, 100 percent of the samples indicated human bacteria. The more conservative test showed human fecal bacteria in 70 percent of samples taken from the Animas at the state line, Aztec, Boyd Park in San Juan County, N.M., the San Juan River at Farmington and Hogsback near the border of the Navajo Nation.

She said test results also showed that in both Colorado and New Mexico, the loads of E. coli, phosphorous and nitrogen often were far greater than the Environmental Protection Agency standard for safe recreation.

Pointing to a graph, she said, “when you zoom in there, we have a bigger problem than the EPA thinks we should. These loads are ten times what they should be.”

It was still unclear why and how human fecal bacteria was entering the water stream, but she said it could be from “direct discharge” or “stormwater.”

“More analysis is needed. At this point, there’s no smoking gun,’” she said.

cmcallister@durangoherald.com