East Sister is the one island of the Erie Archipelago that escaped being logged. Less than a kilometre across, the island supports a rich and distinct ecology. Its southern vegetation includes several plants that are rare in Canada, such as Short's aster and the Kentucky coffee tree. These Kentucky coffee trees shelter a major breeding colony of great blue herons, black-crowned night herons, and great egrets. Other shorebirds, waterfowl and snakes also make the island their home. The archipelago is unique from a geological standpoint. More than ten thousand years ago, a glacier scraped away the topsoil and carved deep scratches in the bedrock. Exposed to the elements of the lake, the island has suffered a lot of weathering. No trees stand along the rocky shoreline and only dense thicket remains in much of the interior. Patches of Silurian and Devonian bedrock, roughly 400 to 430 million years old, have been exposed by the elements. There are no visitor facilities. Because of the possibility of disturbance to the bird colonies, visiting is discouraged, especially from May through August when the heronry is active.