Dan DeVaney (left) and Bill Chelmowski, both with the project office in Fountain City, Wis., prepare to measure ice thickness on Lake Pepin, Minn., on Feb. 21, 2018. The survey crew used an airboat – for both safety and navigability on various ice conditions – to survey each mile on an 18-mile stretch of lake, the widest and slowest-moving segment of the Mississippi River. Measurements take here are the best indicator of spring, as it is the final segment of the river to be clear of ice.