The coast was entirely frozen. There was no way the crabs could get onto shore anymore, unless they climbed the ice or broke through it. Breaking through the ice wasn't possible, as they were already dead the second that they got frozen. Even the ones that were far enough to not get frozen had a hard time getting closer due to the extreme cold that was colder than the south pole's temperature.
Still…
Even when the crabs couldn't approach the beach, they could still find their way to other cities. Jonathan asked Xin Feng was able to freeze the entire lake, but Xin Feng told him that freezing the entire lake wouldn't be a great idea, as a lot of lake lives would get killed, which would be inefficient because unnecessary energy would be wasted to kill harmless creatures.