Rochester, MN (KROC AM News) - A sure sign that spring is on the way took place Wednesday in the Lake City area as a team from the US Army Corps of Engineers climbed aboard air boats and conducted a survey of the ice covering Lake Pepin.

The season’s first measurements found the thickest ice in an area south of Lake City at 19 inches. Last year, the first survey found the maximum thickness was 21 inches, while it was over 32 inches thick in the middle of February in 2014.

Nearly all of the ice on the lake was rated as “blue ice” with only about 1-inch of slushy “white ice” at the surface.

The annual measurements are used by the federal agency to help plan for the start of the 2016 commercial shipping season on the upper Mississippi River. Another survey of the lake is scheduled next week.

Last year, the shipping season opened on March 25th.