Some of the areas along the river's course, especially the
Ōsugi Valley near the source, see a considerable amount of rain each year and thus are very prone to
flooding. Even with modern flood prevention, minor damage from flooding is still seen along parts of the river each year. Flooding from the river was so severe in the past that it was one of the first rivers in Japan to receive a
floodbank during the
Edo era. The magistrate in Yamada (modern Ise) during the
Tokugawa Shogunate felt that the river needed to be controlled because of its proximity to
Ise Grand Shrine, Japan's holiest shrine; he thus ordered work to be done along the river to alleviate the problem. These alterations, which were primarily done along the Yamada-side of the river, were effective in reducing flood damage on that side however increased flooding problems on the other side. Due to the changes made, a bridge across the river was not completed until the
Meiji era. The only significant flooding in recent history was the result of
typhoon #21 in 2004, in which six people died. These deaths occurred in the former village of
Miyagawa, and this disaster was a prime factor behind the village being absorbed by the town of Ōdai soon after. ==Wildlife==