Improvement of River Quality by Sewerage Expansion

This graph1) shows the effectiveness of sewerage system for water pollution control.
As sewer service with treatment grows, BOD of the rivers reduces.
Kamo, Shiba, and Ayase Rivers run through the downtown of Saitama City.

These pictures2) show the rivers before and after sewerage service is in place.

Without sewerage service, the KAMO River was full of foams by untreated sewage.
The left picture was taken in 1978 and the right in 2007 at the same place.

1) http://www.city.saitama.jp/www/contents/1205126406056/files/keikaku01.pdf
2) http://www.city.saitama.jp/www/contents/1205126406056/files/keikaku03.pdf