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E. coli

What is E. coli?

Escherichia coli (E. coli) is a type of bacteria found naturally in the environment that we measure as an indicator of possible fecal contamination and the presence of pathogens. While E. coli is often harmless, persistently high levels can indicate an increased risk of illness when recreating in a waterbody.

How does E. coli get in our streams?

Primary sources of E. coli include waste from pets, urban wildlife, and livestock as well as garbage and faulty sewers and septic systems. Rain and melting snow pick up bacteria and flow directly into local streams without being treated.

Infographic with 4 steps showing how stormwater pollutants travel from our homes into local waterways through the stormwater system.

E. coli in the Boulder St. Vrain watershed

Elevated E. coli levels have been observed throughout the Boulder St. Vrain watershed, similar to other urban streams across the country. Bacteria concentrations can vary dramatically within short time periods and our monitoring program has not observed a sustained increase in E. coli levels in the watershed. Based on available data, the State of Colorado determines which waterbodies have bacteria impairments and where potential issues require further evaluation. Local governments may be required to take specific measures to reduce bacteria in impaired waterways in addition to routine pollution prevention efforts.

As of 2022, 523 miles attain standards, 60 miles need more evaluation, and 149 miles do not meet standards.

What is your community doing?

Your local government works to limit bacteria in our streams in a variety of ways, including:

  • Monitoring water quality and addressing sources of pollution
  • Maintaining pollution control measures
  • Responding to illegal discharges

What can you do?

You can do the following to reduce the bacteria you contribute to our watershed:

  • Pick up your pet waste
  • Secure your trash to keep urban wildlife away
  • Reduce runoff from your lawn by watering sparingly
  • Regularly inspect and maintain your septic system if you have one – visit

How can I recreate safely?

To minimize risk of illness when recreating in local creeks, do not swim in cloudy or discolored water or immediately after a rainstorm. Avoid getting water in your mouth, eyes, or open wounds.

Learn more on the Recreate Safely webpage.