Over-Chlorination

• Pools with high numbers of swimmers, such as public pools, may be over-clorinated. Chlorine kills bacteria and viruses in the water and, while many swimmers can contaminate a pool quickly, maintenance workers sometimes add more chlorine than is necessary to the water to overcompensate for the high traffic. Chlorine can irritate the skin and burn the eyes. Chlorine dries out skin, and research has shown that it acts as a carcinogen in high concentrations.
  
  

Waterborne Illnesses

• Water provides the ideal environment for many types of bacteria and viruses to thrive. Sick swimmers can introduce pathogens into the the water unknowingly, which can then be transmitted to other swimmers. Serious illnesses can result from pool contamination. Swimmers tend to have more eye, ear and nose infections than non-swimmers. Other illnesses that can be transmitted in pool water include cholera, typhoid fever, dysentery and hepatitis-A.
  
  

Overcrowding

• A swimmer in distress can be overlooked by lifeguards or owners in a pool with too many swimmers. Pools with a large volume of swimmers are noisy and have a lot of activity. The screams or frantic motions of a swimmer who needs help can be lost in all of a busy pool's commotion. Limit how many people can be in the pool at once.
  
  

Lightning

• A pool is a very dangerous place to be if a thunderstorm is in the area. Exit the pool as soon as you realize a storm is nearby. If lightning hits a pool with swimmers in it, the electric shock can be fatal. The rule of thumb is not to re-enter a pool for at least 20 minutes after you hear a storm's last thunderclap.
  
  

Drains

• Drains create powerful suction that can hold a person down and cause him to drown, especially a child. Drains have sucked the intestines out of people who have sat on them, and long hair may also get caught in the drain, which can trap a victim underwater. Drains in older pools are often flat with a simple grate over the top--these are the more dangerous type. Newer drains usually have a domed cover with holes over its top and sides. This distributes suction over more area and lessens the pressure. If you are installing a new pool, ask for multiple drains to ease the force on any one drain. Warn swimmers not to play with or near the drains.
  
  

Algae

• Algae is not necessarily dangerous, but can be problematic. Algae grows rampantly in warm water and can cloud the water to the point of turning it green and forming a scum layer. Algae can clog up and stop drains and pool filters and can make the pool susceptible to other microbes. Green algae is common and can cover the entire pool in a slimy film. Black algae is very difficult to kill and usually grows on the sides of pool walls. Black algae is often introduced by swimmers who have worn the same suit in the ocean recently. Yellow algae thrives in shady pools and is resistant to chlorine. Pink algae forms in crevices on the wall; this is called algae but is actually a bacteria.
  
  

Drowning

• Use caution when you swim. It is easy to drown in a pool. Never allow young children near a pool by themselves. Always swim with at least one other person. If you have a medical emergency, such as a heart attack or serious muscle cramp, you could drown. Keep life jackets or flotation devices nearby to throw to people in distress. If you have a private pool, install a fence with a gate that locks to keep people and children out of your pool when you are not able to supervise.