More hazardous is walking across the coral fringing reef to get to the deep water.
Also, there are many riptides across the coral and it is easy to get swept into an "ava (crevice) and into the deep sea. Don't go alone.
Most beaches are owned by the villages next to them and are private. Always enquire and get permission.
Man-made beaches like at the Rainmaker Hotel have sand and a qiet place to swim.
Because American Samoa has a coral fringing reef, there is not too much sand. It is coarse coral sand tht changes to exposed coral until you reach where the waves break andf it drops off into the pacific ocean.
More snorkeling information from a tour company:http://www.wavehunters.com/samoa/samoa_tours.asp