Which of the following germs can cause recreational water illness?

The choice identifying norovirus, cryptosporidium, E. coli, and giardia highlights the key pathogens associated with recreational water illnesses. These germs are known to be transmitted through contaminated water sources, which can occur in pools, lakes, or other recreational water environments.

Norovirus is a leading cause of gastroenteritis outbreaks linked to contaminated water. Cryptosporidium is a parasite that can cause severe diarrhea and is notable for its resistance to chlorine, making it a significant concern in water safety. E. coli, particularly strains such as E. coli O157:H7, can result in serious gastrointestinal illness and may be present in water contaminated with fecal matter. Giardia is another parasite that leads to giardiasis, which can also originate from water sources tainted with feces.

Understanding these pathogens is crucial for lifeguards and water safety professionals, as identifying and addressing risks associated with these germs can help prevent outbreaks of recreational water illnesses and promote health in aquatic environments. The other choices include organisms that may be important in other contexts but are not primarily recognized as causes of recreational water illness.