Yosemite National Park fly fishing
The links provide good information above Andy. In addition to that, try searching the forum using the keyword "Yosemite"
I backpacked Yosemite in early August last year and there is no shortage of fishing in the park although it is not commonly thought of as a Fly fishing destination in the grand scheme of things.
A couple spots in the Valley area would be the Merced at Valley View. The Tuolumne River at Tuolumne Meadows is also a must and these 2 different rivers really give you a great basis to start with. They are also the most popular, but the Tuolumne will be the least crowded as 80% of visitors stay in the Valley. The Dana & Lyell Forks of the Tuolumne are good options too.