CHICAGO (CBS) — The arctic blast has blanketed Chicago in cold and snow.

Lake Michigan can be seen covered with sheets of ice. While it may be stunning to look at, CBS 2’s Mai Martinez reports that firefighters say it’s also very dangerous.

“Stay off the ice, and the ponds and lagoons. It’s not safe ice.”

It’s an important message, but one that’s not always heeded, according to Deputy District Chief Ron Dornecker.

“Even though we’ve had this stretch of cold weather, this ice is not very thick, and it’s not safe at all.”

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Dornecker added that people are going out and testing the sturdiness of the ice. “We’ve had a couple of calls in the last couple of weeks where people have been in and on the ice and we’ve had to go out there and rescue them.”

On average, the Chicago Fire Department responds to about 25 water rescue calls throughout the winter months.

Given how cold the temperatures in Chicago have been, and how cold that makes the water, Dornecker says you don’t have much time “at all” if you fall through the ice.

“You literally have seconds to make a move in this water when you fall through because you’re going to lose your strength, your mobility, your dexterity — the ability to get back onto that ice is going to be really difficult. So you’re going to have 30 seconds or less to get back up on the ice.”

What should you do if you see someone in the water? According to firefighters, call 911, and then if you can, throw that person something that can help pull them to safety.

“Maybe extend something — a pole, a tree branch, a jacket — to the person, help pull them up on the ice. But don’t put yourself on that ice. You’re going to fall through.”

Dornecker says leave the rescue to the professionals, who have the proper equipment and training to help.