I thought the waters I fished the 2nd week of September were pretty crowded, but I think several factors conspired against me.
(1) Slough Creek was closed to access, so all those anglers spilled over to the Lamar and Soda Butte where I was fishing.
(2) With the warm and low water, rivers like the Madison, Firehole and Gibbon hadn't turned on.
(3) I was two week earlier than the timing Hutch suggests.
Even so, I never had trouble finding an unmolested pool to have to myself. I did have anglers walking by, and all but two of them would pass me, and then go past the next good pool and leave it for me before they started fishing on the other side of me. (I'm still mad about the two guys who did not do this.) I talked to Parker yesterday--called his cell thinking he was home and I could return the books he lent me, and he answered from the top of Dunraven Pass! Apparently the bear sow and two cubs my wife went so gaga over is still parked in the same tree with the same traffic jam.
He suggested that Slough Creek had a lot more people on it than I saw, but other waters were quieter than I experienced.
For all I know, August would have been much worse. The good news is that, unlike Maine, there are literally dozens of miles of good water with the fish spread out throughout it, rather than piled up at a few hotspots. That makes even pretty heavy pressure feel different than it does at one of Maine's fall honeyholes. I didn't see anyone hiking in with lawnchairs in the dark so they could occupy the best casting rock for the next 12 hours. (And yes, I have seen that at more than one Maine location this time of year.)