Hold the bridge!

Okay, so there they are, putting explosives near the bridge and they should hold it at all times, just blow it up in the worst case scenario.
Oeh, oh vay... if it should come to that, because they would be cut off from the beach. I look at the small stream of water where the bridge is located and can't help but wonder... No one could swim? It was just a small stream/brook/river and that puny bridge was the ONLY way to cross the water?