It is a little known fact that sea swimming can lead to deafness. This is due to a disorder called surfer's ear. It is a common misconception that it can only affect surfers. It can affect anyone who spends time in the sea. Whether you are a canoeist, wind-surfer, or paddle-boarder you are at risk.
Surfer's ear happens because the wind and sea cool the ear and surrounding area. The body's rather strange response is to grow bony outgrowths around the opening. This gradually narrows the canal. In the early stages people often don't realize that the problem is there. When the canal loses about 90% of it's diameter deafness may become noticeable. Ear infections also become more common because the ear takes longer to dry out. Dirt and flaked skin build up. This makes a perfect breeding ground for bugs.
The problem can be prevented by wearing surfing ear plugs and a waterproof cap. After 10 years of frequent sea swimming without protection most people will have some narrowing. This has been demonstrated by research by ZenPlugs which is on their blog.
Swimming in warm waters doesn't protect you either. Because the cooling is caused by evaporation it still happens in the summer, in warm seas. This means it is important to wear ear protection all year round.