Margerie Glacier is a long tidewater glacier in Glacier Bay, Alaska, United States within the boundaries of Glacier Bay National Park and Preserve. The glacier begins on the southern slopes of Mount Root, elevation , on the AlaskaCanada border flowing southeast down the valley, then turning to the northeast toward its terminus in Tarr Inlet. Margerie Glacier is one of the most active and frequently-visited glaciers in Glacier Bay, which was declared a National Monument in 1925, a National Park and Preserve in 1980, a UNESCO World Biosphere Reserve in 1986 and a World Heritage Site in 1992. While most of the tidewater glaciers in the park have been receding over the last several decades, Margerie Glacier has become stable, neither growing nor receding, while Johns Hopkins Glacier is advancing.