The scary moment happened Saturday on Big Bear Lake, where a throng of ambulances, fire trucks and police cruisers blocked off traffic to save a family of 3 that had somehow made their way onto the frozen surface ... and fell in after the ice gave way.

We're told it appeared the group -- which we're told comprised of a mother, a father and their young daughter -- had apparently wandered out there despite signs clearly saying to stay off the ice. It's unclear how long they were immersed in the freezing water.

Luckily, they were all pulled to safety -- but the way it happened is nothing short of dramatic. Ropes with small flotation devices were tossed across until each one could catch it and be dragged to shore. The child was first, the mother 2nd and eventually the man.