In accordance with Province of Ontario standards, samples are taken at five different spots at a beach, and the geometric mean of those five samples is computed. The Province considers that a geometric mean of 100 or less for the day's five samples is acceptable. This graph shows the annual geometric mean of the daily geometric mean, for each beach, for each year since 1996.
Note: The geometic mean (the nth root of the product of n values) minimizes the effect of large values that are present in the data. The international Blue Flag beach criteria is that no more than 20% of the samples may be above 100. It would be informative to graph the Blue Flag criteria, but those values are not in the data provided by HCHU. However, we are told by HCHU that it is reviewing its reporting procedures, and we hope it will incorporate that change.