This is Takatoki River where the festival participants purify themselves before the festival. The Chawan Matsuri supposed to be held every 3 years, but the lack of funds and people (young ones) has made it much less frequent. 高時川
The area is quite rural, with many rice paddies. May 4 is a national holiday (Greenery Day) in Japan, during Golden Week, a string of national holidays in Japan amounting to a spring vacation.