Stu,
It will be the Derwent if he lives in the Whickham/Swalwell or Blaydon/Winlaton areas of Gateshead. The only other river (besides the Tyne estuary) in Gateshead is the Team, which runs out at Dunston.
There's a load of info regarding the Derwent, and the fishing on it so far this season, on
this thread in the Trout & Grayling Section. Some of it might be of use to you if you come to fish the river.
At this moment in time, an assortment of wet flies and nymphs will give sport on the Derwent during the day, the GRHE, PTN and BWO being the pick. Dries work well in the evening - grey dusters, BWO (early) and sherry spinner (later on) or sedges, depending on whats hatching. If this is your preference, you can worm fish using 'coarse' tackle on
Axwell Park waters in Derwenthaugh Park (Winlaton Mill) and Derwent Park (Rowlands Gill), but
Derwent Angling Association specify that you can only worm fish using fly tackle.
Tight Lines,
wear_n_derwent
Book: The Lambton Worm - The Definitive Guide to Angling in North East England
Website: The Fishing Archives