At Estes Park you will be going for trout - rainbows, brooks, native, etc. It all depends upon how adventuresome you are. We own property out there and have been hitting the Wilderness areas. That means packing in everything including water. Great fishing though and you can have any number of lakes to yourself. Just north of Estes park is the only free running trout stream in Colorado, the Poudre River. This is a great river, and is also used for rafting and kayaking. There are lakes to be fished in the Estes Park itself, but I don't know if there are any guides for the lakes. Mostly, you will find fly shops have guides that will take you to a place to catch trout. There are some other lakes that are great (water reservoirs) if you have a boat and you can troll for the trout. Hope this helps.
Ahoy Colorado, I had lots of luck with a small hook, one or two salmon eggs and a splitshot. Cast into any creek and keep your finger by the spool (spinning gear). Slow the line occasionaly and wait for a tap or no line movement. Set the hook. Ask the local fly shops which flies are working this time of year. The trout can be downright picky.
We also fished large reseivors like Dillon. Waded out with a casting bubble, swivel and four feet of leader. Used #10 and #12 mosquitos. Garden hackle (worms) worked and so did small spinners.
Flush your gear and clothes. Crystal clear moutain streams don't ferment well if left for days. Plenty of bear poop traveling too fast to settle out until it enters the resevoirs and finds your shoes.
If you're following a stream and there are flash flood warnings, CLIMB STRAIGHT UP. You ain't going to out run the wall of water. There would be an unseen cloud burst, many miles away, that will concentrate in your little gorge.