Partially frozen Gurudongmar Lake, a glacial lake located to the north of the Himalayas in the northeast Indian state of Sikkim at an altitude of over 5,150 metres (16,900 ft). The lake is fed by glaciers of the Khangchengyao massif, forms the headwaters of the Teesta river and is considered sacred by Buddhists and Sikhs. Today is Sikkim Day, which commemorates the formation of Sikkim as a state of India in 1975, following a popular referendum and full merger after decades of being a protectorate since 1947.