Aharen Beach is on Tokashiki Island, about an hour ferry ride from Tomari Port in Naha. Great snorkeling and swimming.

If you are staying in Naha, a good alternative is to take the ferry to the Keramas, the collective name for Tokashiki, Zamami, Aka, and several smaller islands. The water in the Keramas is pristine and is known for world class diving and the tourism on the islands is geared for visiting divers. A shallow "discovery" dive for unlicensed divers costs about 10,000 yen.
The ferry leaves from Tomari port in Naha and cost 2,800 yen to 3,540 yen round trip. There is more expensive faster ferry also available. The ferry leaves Tomari Port at 10AM and arrives at 11:10AM. There is a shuttle for Aharen Beach (250 yen) that meets the arriving ferry. The afternoon ferry leaves Tokashiki at 3:30PM or 4PM depending on season.  http://www.vill.tokashiki.okinawa.jp/en