Slap on the eco-friendly sunscreen and get ready to swim to your heart's content. Many of the seas near the mainland are calm, simply because there are so many islands that block the big waves (and water currents) making your swim ever more enjoyable. Hidden lagoons, large gulfs and elevated lakes will also offer you variety for swimming, while the waters will always be milder in temperature than anything you encounter in Europe or North America.
Greece has won many awards for the cleanliness of its beaches, particularly the esteemed Danish Blue Flag award for numerous locations, year after year. Keep the beaches cleaner than you left them, protect yourself against too much sun and enjoy the experience.