Bacteria: Acceptable Levels of E. coli

Fragrant white water lilies, Nymphaea odorata.

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.

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.

	Dissolved Oxygen: Some Isolated Problems Even the successful colonizers zebra mussels (Dreissena polymorpha), seen here covering a submerged tree, survive with difficulty in zones where there is little dissolved oxygen. Dissolved oxygen is a naturally occurring component of rivers and lakes and is essential for all aquatic organisms. These organisms in turn can influence oxygen levels in the water. Aquatic plants and algae produce oxygen through photosynthesis. High levels of fertilizers in the water can cause an overabundance of these plants and algae. Their decomposition by bacteria depletes the oxygen in the water and can lead to dangerously low levels of dissolved oxygen for fish and other organisms. In the Rideau River, oxygen levels in the water fall within the guidelines recommended in the Canadian Water Quality Guidelines for Freshwater Aquatic Life. [11] Nevertheless, scientists found a few pockets of deep water where poor water circulation and high bacterial activity resulted in low oxygen levels. Very few organisms can survive in these conditions, even that otherwise wildly successful invader, the zebra mussel.