In the past week, two snowmobilers have plunged into Rice Lake in Lino Lakes prompting police in the north metro suburb to post signs warning of thin ice and ask snowmobilers to stay off.

“Give them a pretty please with that,” said Cmdr. Kelly McCarthy with the Lino Lakes Police Department. “The signs are not lying. They are not put there as a joke.”

It’s the heart of winter when lakes and rivers should be frozen solid, but with all the warm weather, they are not. And that has authorities across the state spreading the message that ice on many bodies of water isn’t strong enough to support heavy vehicles such as snowmobiles, ATVs and cars.

Even cross-country skiers and anglers on foot can be at risk, said Hennepin County Sheriff Rich Stanek.

“The ice is never safe,” he said. “We’re all for having fun, but you have to be aware of your surroundings. Let’s face it, this has not been a great year for winter sports.”

So far nobody has died, but agencies across the state have reported that a number of vehicles have gone into the water. Last week the St. Louis County Rescue Squad sprang into action when a vehicle fell into Lake Superior near Ashland, Wis.

The Minnesota Department of Natural Resources says at least 4 inches of ice is necessary to support a person on foot, 5 inches for snowmobile or ATV, 8 to 12 inches for a car or small pickup and 12 to 15 inches for a medium-size truck. But it too says, “There is no such thing as 100 percent safe ice.”

The website goes on to add: “Ice may be a foot thick in one location and only an inch or two just a few feet away.”

Snow cover, like this week’s, makes it harder to tell what condition the ice is in.

“The snow masks the ice,” Stanek said. “You can’t tell if it’s 2 feet, 12 feet or 14 feet.”

As of Friday, Lake Minnetonka had an ice depth of 10 to 14 inches, but that’s two inches thinner than last week.

“You would not see me driving a pickup or SUV on any lakes,” Stanek said. “Nothing for sure is safe.”