Excessive and relatively constant moisture in the ear canal can cause infection in the external part of the canal. Infections of this sort are commonly known as "swimmer's ear." The obvious way to prevent swimmer's ear is to keep your ears dry.
If you are prone to swimmer's ear, your doctor may recommend that you wear earplugs while showering or swimming as well drying your ears thoroughly afterwards. Hear Wave Custom Swim Plugs are excellent because they are molded to the contours of your ears, sealing out water better than standard earplugs.