Where the water flows down

Exploration Stage: Tiger's Spring
From: Detective
Description: Buddy, look at that. A vortex-like thing has appeared at the spout! The water is flowing out with the same force as when you pull the plug on the bathtub. Is there a hole in it? If we don't check out that whirlpool as soon as possible, the river in town will dry up completely.
Completed: I examined the mysterious vortex and found nothing of note. Not even a crack in the spout. But when I put my hand in, something black came on it. It looked like wet soot... I don't see anything wrong with the spout, but I'd better look for more!