Corvallis High School sophomore Lars Paulson, 17, held up a test tube filled with water and dropped a tablet into it Thursday morning.

Paulson's teammates, Josh Nelson, 16, also a sophomore, and J.R. Betich, 15, a freshman, were testing the small amount of water for nitrate content.

"We haven't found any nitrates in the samples yet," Paulson said. "If there were nitrates in the water, it would turn red."

The trio were among some 60 students in two biology classes taught by Carole Beedlow and Oregon State University intern Nalish Johnson that are studying the effects of the school's bioswale on the quality of water from the school grounds that flows into Dixon Creek.

Thursday the students were working with Gwenn Kubeck, the city's stormwater program specialist. They recorded results from eight tests: the flow rate of the water, phosphates, nitrates, air and water temperatures, conductivity and turbidity.

The recent lack of rainfall created a small problem - not much water was flowing through the system - but they got enough to perform their basic tests.

The CHS bioswale is a football field long and about 40 feet wide. Its purpose is to capture water during heavy rainfall periods and then release it slowly. The process reduces erosion and also allows plants and other vegetative matter to filter chemicals found in water runoff such as oil from leaky automobile engines, or fertilizer from around lawns.

Carole Beedlow has been teaching science at CHS for 20 years.

"This project allows us to incorporate what we've learned the entire school year," Beedlow said. "We've had lots of support from the city, the school district and the Corvallis Schools Foundation, which provided us with a grant to help purchase testing equipment."

Junior Brynn House, 17, tested a water sample for phosphates, and it came out clean, but sophomore Rosy Phelps, 16, found a small bug in her sample as she tested for turbidity - the amount of suspended particles that makes water cloudy.

"It's a crustacean," Beedlow told her.

House said the water "didn't look too bad," in terms of particulates.

The class findings will be matched with those from another section of biology students, also making the same tests, Beedlow said. Their findings will be announced at a joint meeting June 4.

"We're seeing how effective the bioswale is in improving water quality from the inlet to the outlet into Dixon Creek," Kubeck said. "This is a good educational tool. We need to make people realize that our streets are an extension of our streams. Nearly everything flows into a stream eventually."

In addition to grasses, the bioswale is home to several species of willows, Oregon grape and western red cedars.

Junior Celeste Williams, 17, said the class first tested water from the bioswale a month ago.

"It was running really fast then," Williams said. "It was running about a gallon a minute. The project gives us a chance to get outside. I love it. It's fun, and it's hands on."

Alex Paul can be contacted at alex.paul@lee.net or by calling 758-9526.