River Thames Water Quality Testing Group sites

The River Thames Water Quality Testing Group is operated by volunteers who enjoy wild swimming, paddle-boarding and boating, and are concerned about the water quality in the River Thames and the lack of up-to-date information. Together with several organisations with similar concerns, they conduct tests at a number of river sites between Oxford and Windsor. Visit their website for more information.

Citizen science data from over 14 sites measure two different types of bacteria; Escherischia coli (EC) and Intestinal enterococci (IE).

These bacteria are an indicator of faecal pollution and may be harmful to human health. These are the same bacteria measured at designated bathing waters, and so results are shown against the bathing water thresholds. Find out more about designated bathing waters.

However, three different methods are used to measure bacteria in this dataset:

1. Laboratory testing
   This method replicates the official Environment Agency bathing waters method as closely as possible. Water is collected by citizen scientists in sterile vessels and sent to an accredited microbiology lab where the samples are cultured, and colonies of bacteria are counted. Results come back in 24-48 hours after testing.
2. Petrifilm method
   This method uses the same principle as the Environment Agency method: a sample of water is collected, bacteria is cultured from it and the colonies are counted. Results are available in 24-48 hours. However, the culturing process does not take place in an accredited lab, and smaller sample volumes are used, so the results are less reliable.
3. Field methods
   Some novel methods like Bacterisk and Fluidion provide a much quicker result, either in minutes or hours. These methods employ a very different measurement principle, so are not directly comparable with methods that rely on culturing bacteria.