NEW YORK, June 4 (Xinhua) -- More than 90 percent of popular freshwater fish in U.S. Southern California are carrying human-infecting parasites, posing a significant danger for those who like to eat freshly caught freshwater fish, according to a study published on Tuesday in the Journal of Infectious Diseases.

The parasites are called trematodes. Two species of the flatworms were discovered in California's freshwater fish. The tiny, flattened and sluglike creatures can cause gastrointestinal problems, weight loss and lethargy when a person eats an infected fish. In some rare and severe cases, the parasites have caused strokes or heart attacks.

"Americans don't usually think about parasites when they eat freshwater fish because it hasn't historically been an issue here," the Los Angeles Times quoted Ryan Hechinger, the study's senior author, as saying.

In fact, even when a person has fallen ill from a locally caught infected freshwater fish, their healthcare provider will typically ask if the patient has recently traveled outside of the United States, Hechinger said.