Swimmer's ear is a common disorder amongst those who swim regularly or for prolonged periods of time. It often starts with itching and sore ears. It can progress to pain, discharge, redness, swelling and muffled hearing from dirt clogging the passage of sound. It's medical name is otitis externa. It is caused by the water softening the skin and allowing bacteria carried by the water to penetrate to the underlying dermis layer. Here it might cause infection requiring antibiotic drops. Sometimes oral (tablet or liquid) antibiotics are required in extreme cases.
Prevention is definitely preferable to cure . Wearing a good pair of ear plugs from http://zenplugs.com/molded-earplugs/ for swimming will definitely help to prevent it. Use the early itching as a sign of infection being on it's way; try to swim less often and for shorter periods. When you emerge from the pool or the sea wash your ear canals out with drinking water or surgical alcohol. This will remove dirt and germs. Ensure your ears are clean and you wear your ear plugs every time they are exposed to water.
ZenPlugs Ear Plugs are great for preventing swimmers' ear because users can make them at home in only a few minutes. They are colourful and excellent at blocking water from your ears. They are even antibacterial, actively fighting the bacteria for you.