New Jersey is in a cold snap, and many ponds, lakes and streams have frozen.

But that doesn’t necessarily mean that they’re safe to skate or walk on.

“One has to be really, really cautious when it comes to going out on ice,” said New Jersey state climatologist Dave Robinson.

While it may seem like we’ve been in the deep freeze for weeks, “up until Christmas we were running about a degree above average, so we didn’t have exceptionally cold water ready to freeze when this latest cold spell came through," he said Wednesday.

Mount Olive Mayor Rob Greenbaum knows this is true from first-hand experience. Years ago, two teenagers died after ice fishing on Budd Lake.

“Even through this recent cold snap that we’ve been having you can see that there are areas of the lake that are not covered with ice. In Budd Lake there are currents of warm water; the lake never freezes completely."

He noted while some towns measure the thickness of ice and post safety or danger signs, his town does not. And those who venture out onto a frozen body of water “do so at their own risk.”

“You never know for sure whether it’s frozen through.”

Robinson noted many lakes, streams and some ponds may have currents of water flowing or springs bubbling up that are circulating right beneath the frozen surface. So if you step on them, the ice will break and you’ll plunge into freezing water.

“You can never be fully sure, even after a longer spell of cold. You should always approach the ice with extreme caution.”

He noted it’s not uncommon during the winter to find a body of water in Jersey that’s frozen with 6 to 12 inches of ice in most parts of it, “yet I could still find a part of that pond or lake where there was a spring bubbling up.”

“When water is moving, it doesn’t freeze very readily. Water likes to sit calm and quiet to freeze.

Robinson pointed out that “there are some areas around the state right now where skating and walking on the ice is safe, but there is always that unknown, so never go out alone.”

He said if you do venture out on what you think is completely frozen ice, it’s a good idea to bring a rope and a ladder with you.

“You can never be too cautious because if you fall into that ice you have a very short amount of time to get out before you can get into big, big trouble."

You can contact reporter David Matthau at David.Matthau@townsquaremedia.com