Research and analysis

Experimentally derived decay and growth rates for enterococci in English freshwater environments (EDGE): summary

Published 2 October 2026

Applies to England

1. Chief Scientist’s Group report summary

This project undertook experiments to determine rates of decay for intestinal enterococci (IE) at three freshwater locations. The Environment Agency can now use these newly available rates in bespoke models which will support the understanding of the sources of faecal matter impacting bathing waters.

1.1 Background

There is increasing demand to designate bathing waters in English freshwater environments. The Bathing Water regulations require the Environment Agency to monitor IE and Escherichia coli in designated waters, as indicators of faecal matter.

The Environment Agency uses a bespoke model to evaluate the significance of agricultural inputs of faecal matter in catchments. This model is currently set up for E. coli but not for IE. The inclusion of IE requires relevant experimental data on how concentrations change in the environment over time. Therefore, this project designed a series of experiments to determine these changes at three freshwater locations in England. These sites were the river Thames at Cholsey close to Wallingford Beach, the river Ribble at Edisford Bridge and a lake location at Coniston Water. The overall objective was to quantify the environmental variability in the rates of decay (or growth) for IE from agricultural and human (sewage) sources.

1.2 Approach

Experiments were performed to determine the decay or growth rates of IE from different faecal sources in freshwater sampled from the three locations during autumn 2025. Influent wastewater (i.e., untreated) was added to a set of samples from each location to measure the decay or growth rates of IE from human faeces. Similarly, a slurry prepared from a mixture of bovine and ovine faeces was added to another set of samples from each location to measure the corresponding rates for livestock faeces.

The samples were incubated separately at 5, 10, or 20 °C for 5 days, to determine how decay or growth rates varied with water temperature. The decay rates were derived from these experiments for each location, faecal type, and water temperature, by calculating the times (in days) for the initial population of IE to reduce by 50% and 90%.

1.3 Findings

The main findings were:

• The times for IE to decay by 90% ranged from 1.3 to 6.5 days across different locations, between different waste sources (human vs animal) and different temperatures.
• Growth of IE from untreated wastewater was observed in samples from the river Thames at colder water temperatures of 5 and 10 °C.
• Intestinal enterococci from human wastewater survived longer than those from animal faeces in the river Thames and Lake Coniston at colder water temperatures of 5 and 10 °C. Comparison of these results with the river Ribble experiments and other limited literature values suggests this varies by location.
• The decay of IE from animal faeces was largely independent of water temperature and was comparable between locations.

1.4 Conclusions

These results suggest that decay times for IE in freshwater vary between locations, with water temperature and source. The Environment Agency will use these results to include IE in bespoke models which will be used to further understand how different sources of faecal matter impact the water quality at different locations throughout the year.

1.5 Publication details

This summary relates to information from project SC250004, reported in detail in the following output:

• Report: SC250004/R
• Title: Experimentally derived decay and growth rates for enterococci in English freshwater environments (EDGE)
• Science manager: Joanna Dixon, Chief Scientist’s Group
• Research contractor: Dr Isabelle Fournier, UK Centre for Ecology & Hydrology (UKCEH), Wallingford.

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency