Koremasa Bridge is shown in a few episodes of Your Lie in April, so I went and checked it out.
Image from Episode 1 - 06m22s
There's a soccer field near this pedestrian path and the river is further to the left in real life.
Image from Episode 1 - 06m29s
Kousei, Tsubaki and Watari walking along the pedestrian path.
Image from Episode 9 - 15m03s
In a later episode the same bridge is shown in a flashback.
Image from Episode 9 - 15m26s
Kousei, Tsubaki and Watari as kids.
Image from Episode 9 - 15m40s
You can see one of the transmission towers in the background in the anime shot.
At the nearby Koremasa Station I also saw this poster for anime sightseeing in Saitama. I've marked the path from Koremasa Station to Koremasa Bridge in the map below.
This location was visited on 2016/10/06.
Special thanks to the ones who went here before: