In the 11 times I've been there, (7 in the valley, 4 through Wawona, 1 backcountry) it's never been really good fishing. There are some native fish in almost all of the streams. If it looks like it could hold fish it probably does somewhere. Size and numbers you will generally find disappointing though, especially in the valley where every tourist wets a line. If you flyfish take plenty of both light & dark Elkhair Caddis in #16-10. If spinning try the 2 smallest sizes of Panther Martins. If you go to the "Suspension Bridge"(unsure of actual name) upstream from the Wawona campground try jigging in that deep pool right below the bridge. Last but not least, please practice C&R.

Tight lines,
Wade