Upper Grinnell Lake is located in Glacier National Park, in the U. S. state of Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

. Upper Grinnell Lake is a proglacial lake

Proglacial lake

In geology, a proglacial lake is a lake formed either by the damming action of a moraine or ice dam during the retreat of a melting glacier, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice...

 which formed in the 1930s as Grinnell Glacier

Grinnell Glacier

Grinnell Glacier is located in the heart of Glacier National Park in the U.S. state of Montana. The glacier is named for George Bird Grinnell, an early American conservationist and explorer, who was also a strong advocate of ensuring the creation of Glacier National Park...

 retreated. The lake is oftentimes filled with small iceberg

Iceberg

An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...

s which have been breaking off Grinnell Glacier. Upper Grinnell Lake can be reached by trail and is a 5.5 miles (8.9 km) hike from the Many Glacier Hotel

Many Glacier Hotel

Many Glacier Hotel is a historic hotel located within Glacier National Park, on the east shore of Swiftcurrent Lake. The building is designed as a series of chalets, up to four stories tall, and stretches for a substantial distance along the lakeshore. The building has a Swiss alpine theme both...

.