For many people, a vacation is a time to experience a number of water sports. Unfortunately, much of this is undertaken with little preparation or training. The result is that drowning and water-related injuries are some of the most common causes of death among travelers. We will not try to present here a treatise on water-related injuries and illnesses but merely a listing of things to watch out for.
Regarding swimming, the precautions away from home are pretty much the same as when at home. Do not swim alone. Don't swim in unfamiliar waters without someone who is familiar with them. Don't drink and swim. In addition, it is unwise in tropical countries to swim in lakes or rivers because of the risk of schistosomiasis. This is a disease caused by parasites which enter through the skin. It can result in bowel or bladder disease, chronic liver or kidney failure and even spinal paralysis. Even brief exposure to infected waters such as by rafting or fording barefoot through a stream may be sufficient to result in infection.
There are other infections as well, most notably some deadly amebic infections, which can be caught by swimming in infected waters, even in temperate climates.
Snorkeling is another favorite water pastime. This is fine with appropriate supervision and instruction but again, beware of unfamiliar waters. Waves and currents may be hazardous and certain marine plants and animals can inflict painful and even dangerous injuries. The treatment for specific types of stings (e.g. anemones, coral, etc.) will usually be known by local lifeguards, but rinsing with sea water or vinegar are the common ones. Rubbing, scratching, toweling and washing with plain water may make the situation worse. Injuries from manta rays, biting or stinging fish and shark bites can cause infection or serious tissue damage and usually require prompt medical attention.
Scuba diving, of course, carries a number of particular risks and should be undertaken only with proper instruction and supervision. One should NOT scuba dive when pregnant--any depth or any stage of pregnancy. The changes in air and water pressures can cause serious alteration in fetal circulation. Treatment of decompression sickness (the Bends) almost always requires a decompression chamber but giving oxygen en route can improve the situation.
A relatively new source of serious injury is the jet ski. Too many people, losing their inhibitions while on vacation, take on this sport with poor equipment and no training. Make sure that you get adequate training and use reliable equipment, including life jackets. Most obstetricians feel that it is not a good idea to water ski or jet ski while pregnant. There have been reports of miscarriage being caused by water being forcefully propelled up the vagina.