That's great news for the North Platte.

Could you tell whether the spawning fish were hitting a fly? I had a similar experience on a local high gradient mountain trout stream here in Virginia during the Brook Trout spawning season last fall. The pools there were mostly smaller than my kitchen table so I didn't see hundreds of fish, but I did see dozens. My observations were: a) the spawning fish were very difficult to spook, which is extremely unusual in this type of environment, and b) the spawning fish were not hitting flies, only fish not visibly participating in the ritual woud strike.

I got several pictures, including this one of an apparent love triangle.

Spawners.jpg