January 31, 2005

E coli contamination of L Winnipeg beaches traced to shorebirds

Extensive sampling of Gimli Beach and West Grand Beach, on Lake Winnipeg, last summer has confirmed that shorebirds contribute the largest amount of E coli bacteria to Lake Winnipeg shores. "Extensive samples collected in 2004 allowed for reanalysis of the 2003 data by direct comparison to an expanded database resulting in many of the previously unmatched samples being uniquely matched to shorebirds, including geese," said Water Stewardship Minister Steve Ashton.

The most recent DNA fingerprinting commissioned by Manitoba Water Stewardship reinforce previous data showing shorebirds such as gulls and geese to be the primary identifiable sources of E coli along the beaches. The E coli then makes its way into bathing water from the sand by the uprush and backwash of water into the beach area.

The most recent research conducted by Manitoba Water Stewardship supports the theory that increased E coli readings are shoreline phenomena and do not contribute to E coli densities beyond the swimming area in deeper water. Wet sand underlying beaches harbours E. coli and certain wind conditions will create wave action which occasionally disperses E. coli living in the sand to bathing water, resulting in periodic high E. coli readings.

"Recent and future research activities will significantly enhance our understanding of water quality at the beaches and the largely natural processes responsible for transferring and dispersing bacteria into beach water," Ashton said, adding that, "the data collected during 2004 will be used to develop our early-warning predictive model."

In 2003, 10% of the total sand and water samples could be attributed to shorebirds while approximately 80% of the samples could not be matched to a source. In 2004, approximately 50% of the sand and water samples could be attributed to shorebirds and geese, while 34% of the samples could not be matched to a source.

Improper disposal of food waste on the beach (i.e. littering) attracts gulls and other birds, which in turn contribute to the high levels of E. coli in sand. Major Lake Winnipeg beaches have been routinely monitored for bacteria since the early 1980s. If Manitoba's recreational water quality objective level of 200 E coli per 100 ml of water is repeatedly exceeded, beaches are posted by order of a medical officer of health.

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