Samples of Clear Creek taken during a summer holiday weekend showed a spike in bacteria from human intestines during times of high tubing activity, but the increase was “short-lived,” according to a new study.

Researchers from Colorado School of Mines and Johns Hopkins University took samples from a stretch of Clear Creek in the city of Golden and compared them to an upstream location with relatively little tubing activity. In addition to the increase in bacteria, they found a higher concentration of metals, such as lead, suspended in the water.

The study, first reported by Denver 7, attributed the increase in metals to human activity stirring up the creek bed, where they had accumulated since Colorado’s mining days. The spike in intestinal bacteria suggests that at least some people tubing on the creek also used it as a bathroom.

The authors said the spikes resolved quickly following a high-use weekend, however. They didn’t assess the impact on plants or animal life.