Hotel swimming pools cause 32% of all swimming-related disease outbreaks in the United States, according to new research published by the CDC.

Researchers reported in MMWR that 58% of all outbreaks associated with treated recreational water are caused by Cryptosporidium, which causes mostly diarrhea. Another 16% are caused by Legionella — the agent of Legionnaires’ disease — and 13% are associated with Pseudomonas, which causes skin rashes.

In 46 states and Puerto Rico, there were 493 outbreaks between 2000 and 2014, causing at least 27,219 cases of disease and eight deaths. More than half of the outbreaks occurred from June through August. Most cases (89%) were caused by Cryptosporidium, but at least six of the eight deaths were a result of infection with Legionella.