When consumed in contaminated water, the microscopic parasite Cryptosporidium can cause symptoms of stomach cramps, diarrhea and fever. Now, researchers reporting in the ACS journal Environmental Science & Technology have detected evidence of the parasite in about 40 percent of surveyed wells in public water systems in Minnesota—even wells not influenced by surface water. The team emphasizes that they don’t know whether the parasite levels are high enough to actually cause health concerns.