A glacial lake is a body of water that has been formed by the melting of glaciers. The two crossword solutions for this term are 'TARN' (4 letters) and 'Agassiz' (7 letters). A TARN is a small mountain lake, usually found in a cirque created by a glacier. Lake Agassiz is a large glacial lake that was once located in the northern United States and Canada. It was named after Swiss-American geologist Louis Agassiz.