Swimming in contaminated water may result in skin, eye, ear, and
certain intestinal infections, particularly if the swimmer's head
is submerged. Generally, for infectious disease prevention, only
pools that contain chlorinated water can be considered safe places
In certain areas, fatal primary meningoencephalitis has occurred
following swimming in warm dirty water. Swimmers should avoid beaches
that might be contaminated with human sewage, or with dog feces.
Wading or swimming should be avoided in freshwater streams, canals,
and lakes liable to be infested with the snail hosts of schistosomiasis
(bilharziasis) or contaminated with urine from animals infected
with Leptospira. Biting and stinging fish and corals and
jelly fish may provide a hazard to the swimmer. Never swim alone
or when under the influence of alcohol or drugs, and never dive
head first into an unfamiliar body of water.