Very nostalgic program for me. I used to live in Marlborough Rd in Bounds Green and the New River ran at the rear of our back garden. You couldn't fish it, and couldn't access it due to the concrete railing fence. However it ran quickly and cleanly and held some fantastic fish which you could clearly see due to the quality of the water then.
Wightman Road where he went through the house to try and view the New River was just around the corner from where I also lived in Haringey, I used to walk along Wightman Road to work.
Very near to the above location is Finsbury Park, the lake held some nice carp, but they usually stayed within the sanctuary of the fenced off boating lake. The small area of the lake that could be fished produced some cracking Roach fishing.
Having been nostalgic, I now know why I moved to the country, I don't think I could ever live in London again.