"We don't have a lot of other options," Peter points out tersely. "We stay here, we're dead soon. We hole up somewhere, we're dead later. If we can get off this island, maybe, just maybe we'll find an option that doesn't end with us dead."

If there's no bridge and no boat...he's trying not to think about it. He's not even going to suggest taking one of the tunnels out (hell no). Swimming can't be that hard, can it? People go swimming all the time.