The blanket is supposed to form on the bottom of a filtration tank when a chemical is added to the water. However it often takes a time for the chemical blanket to form and seat itself. It wasn't until there were reports of cryptosporidium that officials began thinking there was a problem with the plant. An interim report by a consultant has recommended additional precautions be taken when there are any irregularities in the testing process. The city's sewage treatment plant is actually upstream from its water plant.
Treated effluent flows downstream into the drinking water intake.
The microscopic parasite, the size of a red blood cell, lives in the intestines of humans and animals and is found in animal and human waste. It can cause temporary gastrointestinal discomfort in those with healthy immune systems. But it is dangerous to people with reduced immune systems, such as those with AIDS or cancer. The three who died had weakened immune systems. 20 elementary school children in Watson Lake, Yukon become ill from water contaminated with E. coli bacteria.