Cryptosporidium is a microscopic organism that is naturally present in most surface water all over the world. When humans or other warm-blooded animals ingest it, Cryptosporidium can cause diarrhea, fever and other gastrointestinal symptoms. Cleveland has been testing Lake Erie water monthly for the presence of this organism for the past several years. Tests have shown the presence of very low concentrations of "empty" organisms (no internal structures) and a few organisms with internal structures. Current test procedures do not show if the organism is still capable of causing illness.