Contamination in the Oklahoma River was to blame for sickening dozens of participants in an international triathlon held last month, state health officials said Wednesday. At least 45 participants in the Boathouse International Triathlon in Oklahoma City became sick with gastrointestinal problems after the event held May 16-17. The Oklahoma Department of Health said the illness was related to exposure to water during swimming practice sessions or during the swim portion of the event. "Laboratory analyses of stool specimens from a few ill athletes were positive for different gastrointestinal agents, including norovirus, and a couple of different kinds of bacteria and parasites, all of which are compatible with this gastrointestinal outbreak and which could be associated with exposure to water contaminated with human or animal waste," the department said in a statement. Athletes swam 1.5 kilometers in the downtown river as part of the triathlon. After the event, some of the participants reported diarrhea, vomiting, abdominal cramping and fever. The river has tested high for bacteria, particularly after high runoff from storms. There were 367 participants in the triathlon. A total of 218 responded to a health department survey and of that number, 45 reported symptoms. "The amount of time spent swimming in the river during the practice sessions and during the event is the only significant exposure associated with the development of diarrheal illness among participants," said Lauri Smithee, chief of the health department's acute disease service. Mike Knopp, director of the OKC Boathouse Foundation, which helped organize the event, said the disease outbreak was unfortunate. "This is a one-time incident that is specific to triathlon, and event organizers will take every precaution to make sure it doesn't happen again," he said. The state Department of Health said a working group of several agencies will study the event to learn how such problems can be avoided in the future.