Cryptosporidium and Giardia are two words that have come up lately in conversations with our cottage owning customers in Manitoba and Northwestern Ontario. These people are interested to know more about Cryptosporidium and Giardia and how to treat their lake water to ensure that they do not get sick. Infection caused by Cryptosporidium is called Cryptosporidiosis, and Giardia sickness is called Giardiasis or “Beaver Fever.” Cryptosporidium and Giardia are both water-borne parasites that infect the intestines of humans and cause diarrhea, stomach cramps, and nausea; symptoms can last 7-10 days for most people who are otherwise healthy. Both Cryptosporidium and Giardia exist as oocysts in untreated lake, stream and river water. These hard shelled oocysts protect the viruses from a wide range of environmental conditions. The best way for cottage owners to avoid contracting Cryptosporidium or Giardia that may be in their untreated water is to use a filter with an “absolute (not “nominal”) pore size of 1 micron or smaller. This will effectively remove Cryptosporidium and Giardia oocysts from water. Due to the hard shelled oocysts protecting these parasites, ultraviolet light and chlorine do not effectively treat them. Once cottage owners have an effective filtration system in place they can enjoy peace of mind knowing that Cryptosporidium and Giardia will not be an issue in their drinking water.