The 196km-long Shimanto-gawa is Japan's last great pristine river. Its waters teem with ayu trout that the locals fish in the early summer. The bridges are built without parapets so that they are simply submerged but not carried away by spates. The sandy islands and banks are thick with vegetation greatly appreciated by herons and egrets. From Nakamura, the town near the estuary, you can rent a canoe-kayak to go up the river.