Native Americans originally knew Sears Island as Wassumkeag, meaning "bright sand beach." Before the causeway was built, a shining sandbar connected the island to the mainland at low tide, and Wassumkeag served as an important navigation beacon for people paddling birchbark canoes around Penobscot Bay. The island's bright sand beach is thought to have helped travelers locate a long-used portage site across the cove on Cape Jellison, avoiding a long paddle around another sizeable body of land jutting into Penobscot Bay. Archaeological evidence confirms that Native Americans began camping on the island more than 3,400 years ago to hunt, fish, and rest along paddling routes, and these remained the island's primary human uses until European contact in the 1600s.