One unique feature in the Borough is Hubbard Glacier, North America's largest tidewater glacier. In 1986 and 2002, the glacier blocked the entrance to Russell Fjord. The resulting Russell Lake rose and until the glacial dam failed. If Russell Lake rises to , the water will spill over a pass and flow into the Situk River. This will have a major impact on a world-class fishery. Yakutat will not be impacted unless the glacier advances to the townsite, which could take a thousand years. The vegetation in the area indicates that water was flowing over the pass until about 1860.