A group of around 15 people began a day of rafting on the Gallatin River Friday collecting aquatic insects and examining them on the river bank.

"We are looking for mayflies, caddis flies and stoneflies," Katie Alvin, assistant director of the Big Sky Institute, told the group. "If we can find all of them then that indicates good diversity and good water quality."

The bug lesson was intended to help the rafters understand the ecology of one of Montana's world-famous blue-ribbon trout streams.

"Water quality and water storage are so important to Big Sky," BSI plant specialist Martha Crocker said. "Not only for the survival of civilization, but because of the immediate threat to fly fishing. It's a huge industry here and it affects tourism."

The institute, created by Montana State University to educate students and the community about the Greater Yellowstone ecosystem, organized the rafting trip to increase awareness of the watershed around Big Sky.

"We want to make science relevant to people," Alvin said.

Once in the rafts, the group, which included tourists of all ages, took water samples at different locations to test for nitrogen, oxygen and pH levels.

They also observed algae levels, which indicate the presence of nitrogen.

"Some nitrogen is necessary, but too much and the water quality drops off," MSU department of ecology graduate student Leslie Piper said. "And with this watershed, even what we're doing up here in Montana can affect the whole country."

The Gallatin is one of the three rivers that merge in Three Forks to form the Missouri River.

Stormwater runoff and wastewater can contain high levels of nitrogen, Alvin said.

Big Sky's wastewater is currently stored and used to water the golf course. Some of the rafters suggested it might also be used to make snow during the winter or for agriculture. The high nitrogen levels in the water would make it a good fertilizer.

One of the rafters, Sue Abraham, of Minneapolis, said she participated in the six-hour rafting and education trip in order to better understand the resource.

"We are all the custodians of the environment," Abraham said. "When you love the outdoors you want to protect it, whether it's at home or somewhere else."

Samantha Booth can be reached at sbooth@dailychronicle.com