Swimming is generally a healthy activity and enjoys a low risk of injury compared with many other sports. Nevertheless there are some health risks with swimming, including the following:
Drowning, inhalation arising from
Adverse water conditions swamping or overwhelming the swimmer or causing water inhalation.
Actions of others pushing under water accidentally in play or intentionally.
Exhaustion or unconsciousness.
Incapacitation through shallow water blackout, heart attacks, carotid sinus syncope or stroke.
Adverse effects of immersion
Secondary drowning, where inhaled salt water creates a foam in the lungs that restricts breathing.
Salt water aspiration syndrome, SWAS.
Thermal shock after jumping into water can cause the heart to stop.
Exostosis which is an abnormal growth in the ear canal due to the frequent, long-term splashing of water into the ear canal. (Known as Surfers' ear or Swimmers' ear)
Exposure to chemicals
Disinfectant Chlorine will increase the pH of the water, if uncorrected the raised pH may cause eye or skin irritations.
Chlorine inhalation; breathing small quantities of chlorine gas from the water surface whilst swimming for long periods of time may have an adverse effect on the lungs, particularly for asthmatics. This problem may be resolved by using a pool with better ventilation, with an outdoor pool having the best results.
Chlorine also has a negative cosmetic effect after repeated long exposure, turning blonde hair green and stripping brown hair of all color, turning it very light blonde. Chlorine damages the structure of hair, turning it "frizzy."
Chlorine will often remain on skin in an anhydrous form, even after several washings. The Chlorine becomes odourous once it is back in an aqueous solution (when salivated on, during a shower, etc.)
Water is an excellent environment for many bacteria, parasites, fungi and viruses affecting humans depending on water quality.
Skin infections from both swimming and shower rooms can cause athlete's foot (boat bug). The easiest way to avoid this is to dry the space between the toes.
Microscopic parasites such as Cryptosporidium can be resistant to chlorine and can cause diarrheal illness when swimmers swallow pool water.
Ear infections, otitis media, (otitis externa).
Unfortunately, when chlorine levels are improperly balanced, severe health problems may result, such as chronic bronchitis and asthma.
Swimmer's own actions
Overuse injury; competitive butterfly stroke swimmers for example may develop some back pain, including vertebral fractures in rare cases, and shoulder pain after long years of training, breaststroke swimmers may develop knee pain, and hip pain, and freestyle and backstroke swimmers may develop shoulder pain, commonly referred to as swimmer's shoulder (a form of tendinitis).
Hyperventilation in a bid to extend underwater breath-hold times lowers blood carbon dioxide resulting in suppression of the urge to breathe and consequent loss of consciousness towards the end of the dive, see shallow water blackout for the mechanism.
Adverse water and weather conditions
Currents, including tides and rivers can cause exhaustion, move swimmers away from safety, or pull swimmers under water.
Wind enhances waves and can blow a swimmer off course.
Hypothermia, due to cold water, can cause rapid exhaustion and unconsciousness.
Sunburn severity can be increased by reflections in the water and the lack of clothing worn during swimming. Long-term exposure to the sun contributes to risk of skin cancer.
Objects in the water.
Propeller damage is a major cause of accidents, either by being run over by a boat or entanglement on climbing into a boat.
Collision with another swimmer, the pool walls, rocks or boats.
Diving into a submerged object, or the bottom, often in turbid water.
Snagging on underwater objects, particularly submerged branches or wrecks.
Stepping on sharp objects such as broken glass.
Dangerous aquatic life
Stings, jellyfish and some corals.
Piercings, sea urchins, zebra mussels, stingrays
Bites, sharks and other fish, snakes, lobster or crabs.
Electrocution, electric rays, electric eels.