In the Sporades Islands, the snorkeling off the island of Alonissos is known for perfect water clarity. The Alonissos snorkeling is also popular for the large number of shipwrecks.
To reach the snorkeling in the Greek Islands by air, start by using the international airline flights into Athens International Airport (ATH). From Athens, there are two major Greek inter island airline carriers and a handful of smaller airlines to consider (such as Sky Express). Most of the islands have at least small airports. While there are many ferry lines that interconnect the islands (such as Bluster ferries), the schedules can sometimes vary greatly with delays; therefore, the inter island flights might be the best option if you are on a tight schedule. Should you plan to take a ferry, make sure to advance-book a fast catamaran and/or hydrofoil ferry. The busiest times of year are from July through September where the number of visitors greatly out number the available air seats and accommodations, so plan accordingly.
Overall, Alonissos is the 14th most popular snorkel dive spot of all 18 snorkeling dives in Greece.