In prepping for my trip to Patagonia (last month) angling-oriented books I read included:
PATAGONIA, Angler Walkabout Series - book 2 (book 1 is about Africa), by Julian Wicksteed, 2014
Argentine Trout Fishing, a flyfisherman's guide to Patagonia, William C. Leitch, 1991 (so a bit dated)...