Bacteria: Acceptable Levels of E. coli
Like phosphorus and nitrogen, bacteria are a normal part of a river's ecosystem. They further the decomposition of dead plants and animals and they convert minerals and nutrients into a form that can easily be used for growth by other plants and animals.
Certain bacteria, such as the fecal coliform Escherichia coli (E. coli), can be dangerous to humans and certain other animals. High concentrations of E. coli can cause illness in humans. The virulent E. coli strain 0157:H7, which can cause death, was not found in the Rideau River by researchers during the Project.
E. coli are washed into the water from nearby manure-fertilized agricultural fields and in stormwater runoff (in cities), or are introduced from improperly maintained septic tanks or by livestock with unhindered access to the water.
Levels of the bacteria E. coli were low enough during most summer days of the Project to permit swimming in the River.
The lowest level recorded during the three years of the Project was about 10 colony-forming units (CFU) per 100 ml. Local regulations set 100 CFU/100 ml as the level at which swimming is not recommended. Federal regulations caution against swimming when the level reaches 200 CFU/100 ml.
Only one abnormally elevated level was recorded, in July 1998. The level was recorded near a water treatment plant, after a severe storm. On this occasion the E. coli level was 380 CFU/100 ml.
|Last Update: 2007-05-18|
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