I know about the section of the River Ash that is a part of Amwell Magna, but wondered whether anyone has tried to fish other sections of this river?

I have seen on the ordnance survey map some sections between Widford and Much Hadham accessible via the Hertfordshire Way.

I had a walk down there but saw no fish, but some sections I guess would be accessible only by wading. The water looked crystal clear but no sign of fish!
Not even sure if you are allowed to fish there..........