This 26-acre island in northern Casco Bay is located east of Orrs Island and south of Cundy?s Harbor. The island is primarily forested with a cleared area on the south side of the island.
Flag Island is a traditional nesting site for a large colony of Great Blue Herons, though numbers have waned here in the last 10 years. This site also is home to the largest nesting colony of eiders in Casco Bay and one of the southernmost nesting sites in their range.
As for all the islands in this IBA, overboard discharge from boats in the harbor as well as the threat of an oil spill in or around the bay, are constant threats.
The site was placed in conservation ownership in 2001. The island is owned by the Maine Dept. of Inland Fisheries and Wildlife. Landing on Flag Island is prohibited during the nesting season (April 15 through July 31 each year).