I just moved here from Denver CO and was a member of the same forum (www.coloradofisherman.com) that Chad LaChance was on back in CO. That dude is a great fisherman. I have also fished the Yampa a couple of times. The Yampa is an amazing river but it is a shame what they are doing to it now. They are trying to remove the Pike and Smallies from the river because they are invasive species. And the Humpback Chub, Pikeminnow, and Whitefish populations are hurting. However there is a group of anglers that have organized and has proven that the chub, pikeminnow, and whitefish are hurting because of habitat loss not predation by pike and bass. Anyway, that is an intense debate back in CO right now.
Here is a link to the state park site that shows the access points: http://parks.state.co.us/Parks/yampariver
You have to think of the Yampa as two different rivers: from Hayden upstream is trout water and from Hayden down is more like traditional warm water fishery- flat water that you can float in a canoe- rare in CO. In the Hayden area you will find trout and you used to start seeing smallies and pike there. However the removals have really been concentrated from Hayden to Duffy Mountain area. So the fishing for smallies and pike in that water is not what is once was. Most of the trout fishermen focus from Hayden upstream. (Don't forget that you can drive to Steamboat and fish some great water right in town!).
From Juniper Canyon on down they cannot access as many places for the removals so Pike and Smallies are abundant. There is no rule FORCING YOU to keep Pike or Smallies that I know of. They ask you to consider but many anglers think that it is only a matter of time before they abandon the removals because they just can't get all the fish out of there. So, lots of guys, myself included, practiced catch and release. You can form your own opinion on that. We straight hammered the smallies on my last float from Duffy Mnt to Juniper Canyon. Beautiful strong and large fish!