E. Coli in Boulder Creek

Escherichia coli (E. coli) are a large and diverse group of bacteria that typically live in the digestive tracks of warm-blooded animals. Most strains of E. coli are harmless, but some can make you sick. Measuring for E. coli is easier than measuring for all possible pathogens in waterbodies, so it is widely used as an indicator of the presence of bacteria and viruses that can make people sick. E. coli concentrations provide information about the possible presence of pathogens but does not provide information about where the E. coli is coming from.

When wading or swimming in any natural water body, including Boulder Creek, you may be exposed to E. coli and other microorganisms. Most types of E. coli do not cause illness, but there are certain strains that can cause gastrointestinal illness and symptoms can include nausea, vomiting, stomachache, diarrhea, headache and fever. Boulder Creek does periodically exceed the level of E. coli deemed safe for recreational use by the U.S. Environmental Protection Agency.

Use these tips to help reduce the chance of getting sick while swimming:

• Don’t get water in your mouth, eyes or open wounds.
• Stay out of the water if you are sick or have a weakened immune system.
• Wash your hands and shower after being in the creek.
• Don’t swim within 48 hours of a rainstorm or if the water looks cloudy or discolored.
• Be aware that small children and older adults may have more risk of contracting serious illness from waterborne pathogens.

Everyone can help reduce pollution in Boulder Creek and other creeks in Boulder. Stormwater run-off goes directly into our creeks without being treated. Trash, debris and pollution you see on streets, sidewalks and parks is therefore likely to end up in the creeks.

• Pick up after your pets at home, in your neighborhood and on the trails.
• Keep trash bins closed and inaccessible to wildlife.
• Replace cracked waste bins, keep street gutters clean from trash and pick up after yourself and your neighbors to avoid attracting wildlife. Contact your property manager if your waste area does not look well maintained.
• Use waterwise landscaping and talk with your neighbors about water conservation.
• Reduce or eliminate lawn and garden irrigation, fix leaking or broken irrigation equipment and keep sprinklers aimed at landscaping, not the sidewalk or road. Report over-irrigation on city properties or broken irrigation equipment on Inquire Boulder.
• Follow Leave No Trace principles when recreating outdoors. Always use restrooms, and always properly dispose of soiled diapers.
• Report illegal dumping or improper waste disposal, and anything but clean water (e.g., paint, chemicals) entering the street, storm drains or any body of water. Report these issues on Inquire Boulder or follow steps to report a spill to the stormwater quality program.
• Visit the Keep It Clean Partnership to learn more about how you can protect water quality by preventing stormwater pollution.

Wildlife

The city has explored using infrastructure designed to prevent raccoons from entering the stormwater system. Due to limited effectiveness, safety concerns and cost, the city determined this was not a viable solution. They city’s Bear Protection Ordinance requires bear-resistant containers if trash and compost are put out the night before pickup.

Pet Waste

The city provides pet waste bag stations and dog waste receptacles. A Pet Waste Removal Fine and educational Let’s Doo It Campaign encourages community members to understand the importance of picking up after pets. About 80,000 pounds of dog waste is left behind on OSMP trails annually.

Trash Management

The city’s Universal Zero Waste Ordinance requires all properties in Boulder to have waste services that provide separated compost, recycling and trash so that waste can be properly managed. The city regularly cleans up creeks and has a restaurant outreach program to promote proper waste and fats, oils and grease (FOG) disposal practices.

Illicit Discharges

The city will continue to operate its robust illicit discharge detection and elimination (IDDE) program and respond to all observed and reported illicit discharges.

Human Sources

The city did not find any direct connections between the sanitary and stormwater sewer systems. However, there was evidence of human sources in multiple outfall investigations. The city saw improper disposal of diapers and human waste and found positive results for human genetic markers in the stormwater system. Human fecal contamination is more likely to cause illness than other sources of bacteria and should be taken seriously.

The city performs routine pipe condition assessments and repairs on sanitary and stormwater pipes. In addition to maintaining properly functioning pipes, these assessments and repairs protect water quality by preventing sewage from directly or indirectly entering Boulder’s surface waters or stormwater system.

The city also regularly performs trash pickup along Boulder Creek, maintains trash receptacles and maintains multiple public restroom facilities adjacent to Boulder Creek. Restroom accessibility has been increased by adding a restroom south of the 6th Street Bridge crossing.

Naturalized E. coli

While E. coli typically lives in the digestive tracks of warm-blooded animals, it can become naturalized, which means it will exist in the natural environment on its own. This means that once E. coli is present in an area, like in the stormwater system pipes and on the stream bottom, it can continue to grow. This results in more E. coli, beyond what has been introduced by the other listed bacteria sources. While naturalized E. coli found in the environment is less of a health risk than E. coli from fecal contamination, it is not possible to differentiate between the two. The best use of time and resources for the city and community is to focus our efforts on controllable sources of bacteria.

Dry-weather Flow

Dry-weather flow is water in the stormwater system that did not come from rainfall. While not a direct source of E. coli, dry-weather flows can mobilize E. coli in the stormwater system and flow into Boulder Creek. The most common sources of dry-weather flow included:

• Groundwater: Groundwater from building foundation drains or sump pumps frequently discharges directly to stormwater pipes. While this is allowed when dewatering permit requirements are met, directing groundwater to landscaped areas is preferred.
• Ditch conveyance: Some of our stormwater pipes are designed to also transport irrigation water either to downstream ditch users or return unused water back to Boulder Creek. The city is exploring opportunities to improve infrastructure and limit unnecessary irrigation return flows where feasible.
• Irrigation overspray: Irrigation water from both residential and commercial properties was seen to be entering the stormwater system. Overwatering can be eliminated through proper management.

Sources of dry-weather flow are dispersed and episodic and are sometimes necessary (groundwater sump pumps). No single solution will eliminate dry-weather flow in the stormwater system. The city assists in repairing leaking ditches, implementing the city’s Water Efficiency Plan, supporting community water conservation efforts and maintaining irrigation equipment on city properties. The most effective dry-weather flow reduction strategy is a combined effort between the city and the community.

The City of Boulder’s stormwater group has routinely monitored the health of Boulder Creek for over 30 years. Boulder Creek E. coli is currently monitored at least monthly at six locations within the city. This monitoring allows the city to evaluate current conditions, examine long-term trends and better understand the health of Boulder Creek as the city grows and changes.

In addition to routine monitoring, the city has conducted outfall investigations to further understand Boulder Creek’s E. coli levels. Outfall investigations have focused on identifying sources of E. coli from priority stormwater pipe networks that drain to Boulder Creek following the steps outlined in the 2019 E. coli Total Maximum Daily Load (TMDL) Implementation Plan. The plan and other study reports can be provided upon request.

The city’s stormwater group plans to continue routine E. coli monitoring in Boulder Creek and investigating possible sources of E. coli, particularly any evidence of human waste. The city is currently reviewing and compiling findings to date from five years of implementing the 2019 TMDL Implementation Plan. This analysis will inform specific next steps for the program and will be shared on this web page by the end of 2024.

Boulder Creek E. coli Long-Term Trends

Bacteria concentrations can vary dramatically within short periods, but the following trends for Boulder Creek have been identified using the city’s routine E. coli monitoring data.

• E. coli concentrations remain stable: monitoring data does not show E. coli increasing or decreasing in Boulder Creek over time.
• E. coli generally increases as you move downstream. In other words, levels of E. coli typically increase as Boulder Creek flows west to east through the city.
• E. coli concentrations are typically highest in late summer and fall. Warmer temperatures and lower flows in Boulder Creek at this time are more favorable for E. coli.

Additional results and discussion can be found in the Keep It Clean Partnership water quality report.