The Popponesset Spit is a fragile, natural barrier peninsula and wildlife sanctuary that protects Popponesset Bay from Nantucket Sound, Mashpee’s watershed, and other lands throughout Mashpee and Cotuit. The Popponesset Spit is owned and protected by the local non-profit organization, Save Popponesset Bay (SPB), and the Massachusetts Audubon Society.

Thatch Island is at the end of Popponesset Spit.