Aegina's position in the Saronic Gulf gives it reliably warm water from June through September and afternoon sea breezes that arrive most days with enough consistency to make windsurfing worthwhile. The beach at Agia Marina, on the east coast, has the most organised water sports setup on the island, with rental equipment and instruction available through a couple of concessions that operate from late May until early October. Beginners will find the bay's relatively sheltered conditions forgiving; more experienced sailors can head further out where the wind picks up.
Paddleboarding has become popular on Aegina in recent years, particularly in the calm mornings before the wind builds. The harbour area of Aegina town and the bay at Marathonas are both good spots for beginners to get comfortable, with flat water and easy access in and out. Stand-up paddleboards can be hired by the hour from several points along the seafront in Aegina town. For something more adventurous, paddling the short crossing to the islet of Moni from Perdika on a calm morning is well within reach for anyone with a basic level of fitness.
Snorkelling requires no equipment hire if you bring your own mask and fins, but sets are available from a few beach shops for reasonable prices. The rocky sections of coastline, particularly around the southern tip of the island and the sea caves near Sfentouri, hold the most interesting underwater scenery. Sea grass beds, rocky outcrops, and the occasional sandy channel create varied habitat. Octopus, sea bream, wrasse, and starfish are common sights. The water visibility in the Saronic Gulf is generally good, often exceeding fifteen metres on calm days.
Kayaking tours are offered by at least one operator based in Aegina town during the summer season, combining paddling with stops at coves and a commentary on the island's history as seen from the water. These tend to run in the morning, departing around eight before the afternoon breeze complicates things. Booking ahead is advisable in July and August, as group sizes are small and spaces fill quickly.