E. coli Monitoring

Division of Water Quality monitors sample for E. coli from May through October every year.

The primary objective of the Division of Water Quality (DWQ) E. coli monitoring program is to monitor popular swimming and recreation areas to determine whether they have high levels of E. coli. If problems are discovered through testing, DWQ and cooperating partners such as local health departments conduct follow-up monitoring and look for areas that might be contributing bacterial contamination to a waterbody. This is a difficult task because E. coli pollution can come from many different sources and be spread throughout a watershed.

DWQ uses the presence of E. coli as an indicator to monitor for the potential presence of more harmful microbes such as Cryptosporidium, Giardia, Shigella, and norovirus. Pathogens often co-occur with indicators of fecal contamination. Because it is not feasible to test waters for each possible type of disease-causing bacterium or parasite, fecal indicator bacteria such as E. coli are sampled to indicate the statistical likelihood of contracting a disease by ingesting or recreating in waters. Although not all E. coli bacteria are typically pathogenic, extensive studies have demonstrated that E. coli concentrations are one of the best predictors of gastrointestinal illnesses associated with swimming in untreated surface waters.

Monitoring Schedule

The Division of Water Quality (DWQ) and cooperating agencies routinely monitor for E. coli around the state during the recreation season from May through October. This monitoring is conducted as a part of numerous different water-quality programs including Total Maximum Daily Load (TMDL) development for waters impaired by E. coli, targeted watershed monitoring, recreational monitoring, and nonpoint source projects.

DWQ works with local health departments to prioritize water bodies for E. coli monitoring, focusing on areas that receive the highest recreation use. Current monitoring plans include sampling targeted waterbodies once a month from May through October. More frequent sampling may be required at specific waterbodies when the data suggest that E. coli densities are high. Ideally, DWQ and its partners would be able to collect samples weekly at all locations. But with limited monitoring resources, sampling for potential E. coli contamination focuses on areas where people recreate most frequently.

E. coli sampling at non-priority rivers and streams uses targeted rotating basin schedule. Less frequented lakes and reservoirs are scheduled on a rotating basis as well.

State Water Quality Criteria

Water samples in special trays to determine the presence of E. coli

Utah uses the Most Probable Number (MPN) method to estimate the concentration of E. coli in a water sample. The presence of a high number of indicator organisms such as E. coli signals a higher probability of pathogens in the water. The threshold of 409 MPN of bacterial density per 100 milliliters (mL) of water relates to a risk factor of 8 illnesses per 1,000 swimmers. As the value of the MPN increases above 409 MPN, the risk of illness if exposed to contaminated waters also increases. Sample results above 409 MPN can result in advisories until further sampling demonstrates that E. coli levels have decreased below this maximum level.

Samples are collected using strict sampling protocols. Samples brought back from the field are incubated for 24-28 hours in individual wells in special trays. Scientists count the number of wells that turn both fluorescent and yellow and run this number through an MPN generator to determine the MPN counts per 100 mL of water.

2019 E. coli Monitoring Plan

The DWQ Statewide E. coli Monitoring Plan is a summary of surface water E. coli monitoring around the state and includes sampling plans from DWQ programs, as well as external cooperators.

Rotating Basin Schedule

Watershed 2019 2020 2021 2022 2023 2024
Colorado Basin
Sevier-Beaver-Cedar
Bear River
Weber River
Uinta Basin
Jordan River/Utah Lake