General Fecal Bacteria/E. Coli Questions

Do all waterbodies have bacteria?
Yes.  Healthy ponds, rivers streams and lakes usually contain a variety of microorganisms, including bacteria, viruses, protozoa, fungi, and algae. Most of these occur naturally and have little impact on human health. Most are beneficial, serving as food for other organisms, and playing critical roles in organic matter breakdown, and nutrient cycling. Some microorganisms, however, can cause disease in humans.

What is E. coli and is it dangerous?
Escherichia coli or E. coli is a type of bacteria commonly found in the intestines and feces of healthy warm-blooded animals and humans.

While many strains of E. coli are not generally harmful themselves, their presence indicates the potential presence of harmful strains and other possible disease-causing bacteria or viruses in water.

What are the sources of bacteria, including E. coli, to the Boise River and City ponds, and how does it get into the water?
E. coli comes from animal and human waste from such sources as domesticated animals—including dogs and livestock, large concentrations of waterfowl and other wildlife, improper waste dumping, faulty septic tanks or sewer systems.  Pollution of all kinds, including E. coli, are typically higher after rainstorms since water draining into ponds and rivers travels over lawns, farm fields, sidewalks, and streets, which may contribute sources of fecal contamination.

How does dog fecal matter get into waterbodies if the dogs don’t actually poop in them?
Dogs don’t have to directly poop in the ponds for their fecal bacteria to become a problem.  In fact, while possible, it is probably rare that this happens. Direct input can occur when fecal matter is stuck on their fur and on their feet.  The most common entry method is runoff carried by sprinklers and other stormwater inputs (runoff following a rain event).

How much bacteria is in poop?
One gram is about the weight of a business card. One gram of dog poop contains 23 million fecal coliform bacteria.  Goose poop has approximately 10,000 fecal coliform bacteria per gram of feces.  An average-size dog pile contains 3 billion fecal coliform bacteria, significantly higher than most other animals.

If dogs were identified as the source of fecal bacteria to the ponds, does that mean my dog is sick and should be tested for E. coli?
No.  E. coli is a type of bacteria commonly found in the intestines and feces of healthy warm-blooded animals and humans. If your dog has diarrhea or is vomiting, contact your veterinarian.

Is the presence of human fecal matter in the water common at public swimming beaches?
Unfortunately, it is not rare.  In many lake or beach monitoring programs major sources of fecal bacteria have been identified as domesticated animals and pets, wildlife, and humans.

Does the City of Boise routinely test for E. coli bacteria?
Yes. The City worked with the Idaho Department of Environmental Quality and Central District Health in 2013 to formalize monitoring, reporting, and public notification procedures.  The City collects samples at City-owned ponds specifically designated for swimming weekly, April 1 – September 30th.

If E. coli concentrations are above Idaho water quality standards for recreational use (30-day geometric mean of 126 CFU/100 mL), or if a single sample is above a level identified to monitor public swimming areas more closely (235 CFU/100 mL), samples are collected daily (M-F) to track bacteria levels.

How does the City decide if the ponds are safe for swimming?
The Idaho water quality standard for recreational use (including swimming and wading) is based on E. coli concentrations in the water. The City of Boise monitors E. coli concentrations in the ponds weekly during the primary recreational season (April 1 – September 30) and will post warnings or close the ponds if concentrations are above water quality standards or levels identified to more closely monitor public swimming areas.

For water to meet the recreation standards, the geometric mean of 5 samples collected 3-7 days apart over a 30-day period is required to be less than 126 colony forming units (CFU)/100 mL.  There is a second part of the criterion that addresses single sample values.  The thought is that if a water sample exceeds the E. coli single sample maximum, it likely exceeds the geometric mean.  The exceedance of the single sample value is not alone a violation of water quality standards; it initiates the requirement for more samples to be collected to calculate the 30-day geometric mean.  The single sample value for waters specified as public swimming beaches in Idaho is 235 E. coli organisms per 100 ml.  The standards also state “Single sample counts above this value should be used in considering beach closures”.  

What are the levels of E. coli in the Boise River?
The City also monitors E. coli in the Boise River weekly June 1st through September 30th at Ann Morrison Park and monthly at Veteran’s Memorial Parkway Bridge and Glenwood Bridge year-round.  In 2014-2017, E. coli concentrations in the Boise River were higher than in Quinn’s Pond.

Seasonal average E. coli concentrations (MPN/100 ml) 2014-2016 in Quinn’s Pond and the Boise River at Ann Morrison Park, and 2017-2018 in Esther Simplot Pond.






Quinn’s Pond






Esther Simplot Pond 1






Boise River at AM Park






Although it is only monitored monthly, E. coli concentrations in the Boise River at Veteran’s Memorial Parkway (downstream of the ponds) April through June have been fairly low 17.0 – 53.8 MPN/100 ml in 2018.  Between 2014 and 2017 E. coli concentrations at the Ann Morrison Park sampling location (upstream of the ponds) have been variable, ranging from 4.1 to 270.0 MPN/100 ml.  In 2018, the highest concentration of E. Coli was 78 MPN/100mL in August. During that time Quinn’s Pond E. coli concentrations were on average 35 MPN/100 mL, and it is unlikely water entering the pond from the Boise River via groundwater is causing the high concentrations observed in the ponds.

Why was microbial source tracking (MST) conducted?
Microbial source tracking (also called bacteria or fecal tracking) was conducted to identify dominant sources of fecal bacteria to the Esther Simplot Park ponds and Quinn’s Pond.

The particular technique of microbial source tracking was chosen because it provided source identification results within 10 business days allowing the City to make informed decisions quickly.  Other methods commonly used in watershed analyses take months to receive results.

Microbial source tracking techniques are not regulated by the Environmental Protection Agency however, MST techniques have been used by many states, including Idaho, to identify sources of fecal bacteria in watershed clean-up programs.

Were the microbial source tracking results the only evidence of dogs as a predominant source of fecal bacteria to the ponds?
No.  Field investigations and poop clean-up activities revealed large amounts of dog poop, as well as goose poop, in the Parks and around the ponds. In addition, park users have voiced frustration with dog owners who do not clean up after their pets.

How can I reduce my risk of E. coli exposure?
To reduce potential health risks, you should assume all surface waters contain some E. coli whether or not it has been monitored or an advisory has been issued. This means you should try not swallow the water, or if you have touched the water, make sure to wash your hands before you touch your mouth or eyes. The single most important way to prevent person-to-person spread of E. coli is careful hand washing.

Are the fish OK to eat?
Yes. Because fish are not warm-blooded, E. coli cannot live in the fillets. However, the water covering the fish could contain E. coli, as well as the guts of the fish. Uncooked fish may well have E. coli contamination. Wash and cook the fish, and wash your hands after handling fish, tackle and pond water to reduce your risk.

What is being done to reduce the E. coli?
The primary objective of the City of Boise’s E. coli monitoring program is to monitor swimming areas for safe E. coli levels. When the concentrations increased, additional monitoring occurred to identify areas that might contribute to bacterial contamination.

Once the sources are identified, problem areas and strategies to reduce pollution can be implemented.

To mitigate the source of the bacteria, the City of Boise will no longer allow dogs at Quinn’s Pond or Esther Simplot Park, including the ponds and the previously designated dog off-leash area. The City is also using goose hazing techniques in the ponds in order to move them out and is increasing the frequency of goose feces removal at both parks. There has been an effort to reduce runoff by adjusting irrigation and increase planting of grasses and plants. Finally, the Boise Parks and Recreation Department will continue to educate the public about the importance of using swim diapers when children are recreating at the ponds.

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