Why does it matter?
The detection of fecal coliform bacteria (including E. coli) in water indicates recent fecal contamination. This suggests that other fecal pathogens (e.g., parasites and viruses) may be present, which can pose a health risk to people.
The amount of E. coli in lakes and rivers is often used to assess the safety of water for recreational purposes such as swimming, boating and fishing. It is also an important measure of drinking water quality.
Fecal coliform bacteria typically don’t survive more than a few days in a river or lake. If there are infrequent inputs of fecal coliform (e.g., following heavy rains that cause stormwater and agriculture runoff) then we would expect to see high bacteria counts for a few days and low counts the rest of the time.
If fecal coliform levels are consistently high, it indicates that the source of contamination is entering the water regularly.