Pueblo health officials say unexplained, random jumps in the levels of bacteria in Fountain Creek underscore the need to keep checking the creek.
Health officials have been checking the levels of E. coli in Fountain Creek and the Arkansas River weekly since tens of thousands of gallons of raw sewage from Colorado Springs spilled into the creek last year.
The state fined Colorado Springs more than $100,000 for the spills.
Colorado Springs said the spills occurred when flooding overwhelmed its system.
The average bacteria count in the creek and river is below the maximum rate allowed by the Environmental Protection Agency.
But health officials can't explain high levels found at different places and times in both the creek and river.