The Minnesota Department of Natural Resources is warning people to be cautious when venturing out on ice.  The agency said walking across frozen lakes is never 100-percent safe, and an average of three people die every year.  No one has died this year, but several people have fallen through frozen lakes.  The majority of those people were taking large ATVs, which require ice that’s at least eight-inches thick.  The DNR urges people to frequently measure ice thickness.