Ōmori Beach of Memories Park (大森ふるさとの浜辺公園) 大森ふるさとの浜辺公園
White sand brought from Shōdoshima, and no swimming: the river next to it pollutes the water
Opened on the first of April 2007, twelve and a half hectares including the water, it was the first park run by a Tokyo municipality with a sand beach and a tidal flat inside it. The area was seaweed country: nori was grown and dried here and sold throughout the city, and a museum opened on 6 April 2008, the Ōmori Nori-no-Furusato-kan, keeps the tools of that trade. The swimming ban is not generic caution, and the municipality states the reason: waste water ends up in the Uchikawa canal, which flows out right next to it, and the water quality is not good enough for bathing.
Tokyo
Heiwajima, Ryutsu Center
https://theanimetrip.com/luoghi/omori-furusato-no-hamabe-koen