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What are Cryptosporidium and Giardia?

Cryptosporidium and Giardia are microscopic organisms that are commonly found in lakes and rivers. They can also be found in recreational waters, such as swimming pools, and in daycare and healthcare settings. Sources of these organisms are animal waste and sewage. When ingested, Cryptosporidium and Giardia can cause gastro-intestinal disease, including diarrhea, cramping, and fever.

Because of our protected watersheds, levels of Cryptosporidium and Giardia in Seattle’s raw water supplies are very low and in most samples they are not even detected. In our water treatment facilities, the water supplies are treated for Cryptosporidium and Giardia using filtration and disinfection processes. For more information about SPU’s water treatment, see the Cedar Water Treatment Facility and Tolt Water Treatment Facility.