The Senshu region is dotted with reservoir ponds, some 3,500 of them accounting for 60 percent of the reservoirs in Osaka Prefecture. The prefecture itself accounts for 1/20th of reservoirs in all of Japan. Collecting water from local streams, these reservoirs are used to irrigate agricultural land through a vast web of irrigation channels.
The reservoirs of Senshu have a long history going back to the introduction of wet rice culture in the Yayoi period (300 BCE–300 CE). In the Nara period (710–794), the Priest Gyoki (668–749) was instrumental in building these reservoirs, saving the people from recurrent drought and continuing that role even today.
The reservoirs are maintained by their respective communities, and in recent years they have gained renewed recognition as the focus of citizen-participation in water-related recreation facilities. Nagaike Oasis, one of the “100 Select Reservoirs,” is encircled by a walking route.