Most of it is on the rez, except for maybe the last 40 miles before it
reaches the Yellowstone. Living and fishing in MT my entire life
(Billings), I never got into the Bighorn fishing thing.

As Bob stated, it's a warmwater fishing environment. Though the trout
get big, they often act sluggish and unhealthy, and if you were to eat a
fish from the waters, the meat is applesauce-mushy and tastes funny due
to water temp.

If you find yourself in that area, I'd suggest driving a couple of
hours west and fishing the cool, clear mountain streams where even the
smaller trout battle like champs. Not to mention the scenery is MUCH
better. Many areas on the 2 Bighorns are treeless plains and miserably
hot. But if you like touristy stuff...there you go.

All that said....Custer died for your sins.