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.

The Mass Audubon Popponesset Spit Wildlife Sanctuary, 5 acres, is situated on the eastern end of the sandy peninsula that separates Popponesset Bay from Nantucket Sound. The remaining 12 acres of the peninsula are owned by Save Popponesset Bay, Inc.

Thatch Island is at the end of Popponesset Spit.