Garbage accumulating in flood reservoir.
Along Kandagawa, one of the rivers I used to run along, one can observe one of the visible signs of an hidden kind of infrastructure dealing with one the naturals disasters the Tokyo area has to deal with, flooding.
When the water rises due to large amount of rains being led to the river the river overflows.
The diagram explains how the water is pumped from one river to another to even out and prevent flooding.
Another sign road sign close to the next river to the north, Zenpukiji-gawa.