"This way, I think" says Tom from down the western side-passage. "Judging by that bridge, I wouldn't be surprised if this loops back, but if it doesn't..." he trails off and turns to look further down the side passage, lingering just long enough to make sure everyone gets across the stream safely before pressing onward.

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I think Tom's already crossed the stream, which would imply that it doesn't require a check to cross. If it does, Tom will use the help action to assist anyone across. If Tom needs to make a check, let me know.

Also, just want to make sure that the side passage walls do become dry after a while.