Isle au Haut is the largest island in this IBA spanning approximately 2,700 acres. The southern portion of the island is predominantly in federal ownership and includes a small tent-only campground and numerous hiking trails. The northern portion is largely privately owned with about 35 year-round residents swelling to over 200 residents during the summer. The bold rocky shoreline rings this island with numerous cobblestone coves and a few high cliffs on the most exposed headlands. The island is predominantly a mature maritime spruce-fir community.
The complex shoreline provides abundant habitat for a diverse array of seabirds, shorebirds and ducks. This site is probably the most significant location for wintering Purple Sandpipers and Harlequin Ducks in eastern North America. The abundance of food resources and low disturbance make interior habitats favorable to eagles and landbirds as well.
Development in the northern portion of the island could threaten habitats and, in turn, some birds with increases in disturbance from recreation, land use, pets, etc. Another threat is the introduction of non-native species, both birds (e.g., game birds) and mammals (e.g., raccoons, furbearers, etc.). Although the potential for wildfire is a concern, disturbance to birds from a fire would be temporary. New habitats would quickly recover in burned areas, and would likely create a mosaic of plant communities. The potential for a hazardous spill or pollution from discharge of ballast is ever present.
Ownership is a complex of private and Federal property. Conserved lands here are owned and managed by Acadia National Park. Access to the island is by boat from Stonington.