This is Fukagawa river (深川). If you want to see sakura without crowd or noise, this is the place.
Tourist info: Fukagawa is located in the Koto ward, Tokyo. Inside Fukagawa is a very famous Buddhism temple "Fukagawa Fudo-son." Many Japanese and foreigners visit the temple.
Fukagawa literally means "deep river," which is not exactly true for this river. Alongside of the river, there are many sakuras planted.
Access:
0. From Tokyo station.
1. use Marunouchi line (metro) to Ootemachi Station. (1 minute)
2. use Tozai line (metro) to Monzen-nakamachi Station. (6 minites)
3. walk north (10 minutes)