Nobody is going to give you a blue line. If a creek is good enough to write about by name, it’s good enough that naming it ruins it. So this isn’t a list of secret spots — it’s how I find my own. The finding is most of the fun anyway.
I do almost all of it from my couch in Colorado Springs with a map open, long before I ever load the truck.
The short answer
To find your own blue lines in Colorado, open a topo map and pick the small perennial creeks (solid blue lines) branching off rivers you already know, then filter them for gradient, cold high elevation, connection to a known fishery, and legal public access — USGS topo maps for the terrain, the CPW Fishing Atlas for regulations, and onX or CalTopo to sort public from private. Do that homework from the couch first, build a short list of three or four, then go look — half will be duds, and the one in ten that’s a gem is the whole point.
Read the Map
The name “blue line” is literal. On a topographic map, every flowing creek is a blue line, and the small unnamed ones branching off the rivers you know are where you start looking.
A few tools do the work:
- USGS topo maps — the classic. Shows gradient (how tight the contour lines are), elevation, and whether a creek runs year-round (solid blue line) or dries up (dashed).
- Colorado Parks & Wildlife Fishing Atlas — free, and it overlays public access, species, and any special regulations onto the map. Start here for legality.
- onX or CalTopo — for sorting public land from private. This matters more than anything else on the list. A great creek you can’t legally reach is worthless.
The whole first pass happens at home. I’ll spend a winter evening with onX open, dropping pins on creeks that look promising, cross-checking gradient against access, building a short list of three or four to go look at once the snow’s off. By the time I actually drive out, I’ve already eliminated the obvious duds — I’m not exploring blind, I’m confirming a hunch. That homework is the reason a scouting trip ends in fish more often than it ends in a shrug.
What Makes a Creek Worth the Hike
Not every blue line holds fish, and not every fishable one is worth the walk. Here’s what I look for before I commit a day to it:
| What | Why it matters |
|---|---|
| Gradient | Some drop, not a waterfall. Tight contour lines = pocket water and plunge pools. Too steep and it’s all whitewater; too flat and it’s a marsh. |
| Perennial flow | A solid blue line that runs all year. Dashed lines dry up by August. |
| Elevation | High enough to stay cold through summer. Cold water holds trout when the lowland creeks get too warm. |
| Connection | A creek that feeds or drains a known fishery often shares its fish. Trout move. |
| Access | Public land, a legal way in, and a hike most people won’t bother with. The walk is your crowd control. |
When a creek checks most of those boxes, it goes on the list. Then I go look.
My take
Half the blue lines I scout turn out to be duds — too small, too warm, too hard to reach, or just plain empty. That’s not failure, it’s the cost of admission. The one in ten that’s a gem is worth the nine that weren’t, and nobody can hand you the shortcut. That’s the entire point of the exercise.
Gear, flies and tactics — the short version
You do not need a second kit for this, but you do need a smaller one. A short glass or graphite rod, a click-pawl reel, a 7.5–9 foot leader in 4X–5X, and one box of mostly dry attractors. If you’re carrying a tailwater rig up a mountain, you brought the wrong thing.
That’s the whole answer at the altitude this post lives at. I wrote the full setup — the specific rod, the reel, the leader spec, what actually goes in the box, and the approach and casting that make it work — in my blue-line gear and tactics guide. This post is about finding the water; that one is about fishing it once you have.
The one thing worth repeating here, because it changes where you point the truck: these fish are opportunists, not critics. Nothing you find will be defeated by fly selection, and everything you find can be ruined by your approach. If a pool goes quiet, it’s almost always because they saw you.
Frequently asked questions
How do I find blue lines if nobody will tell me where they are? That’s the method, not the obstacle. Open a topo map, find the small perennial creeks branching off rivers you already know, filter for gradient, elevation, and public access with onX or CalTopo, then go look. The scouting is most of the reward.
Are blue-line trout easy to catch? Easier to fool, harder to approach. Wild creek fish rarely see flies, so they’ll eat a well-presented attractor without much fuss — but they spook at a shadow or a clumsy step from twenty feet out. The challenge is the stalk, not the fly selection.
Is it legal to fish small unnamed creeks in Colorado? Often, but check first. Public-land creeks are generally open; some are catch-and-release, seasonally closed for spawning natives, or inside cutthroat-recovery areas. The CPW Fishing Atlas and your license spell it out — read before you go.
The Ethics of Blue Lines
This part matters more than the fishing. Small streams are fragile, and the wild and native fish in them — especially Colorado’s cutthroat — can’t absorb pressure the way a stocked tailwater can.
- Don’t name them publicly. Not on the internet, not in a geotag. A blue line stays good because almost nobody knows about it.
- Check the regulations first. Some Colorado streams are catch-and-release, some are seasonally closed to protect spawning natives, some are part of cutthroat recovery areas. The CPW Fishing Atlas and your license cover this — read before you go.
- Handle fish fast, keep them wet, and pinch your barbs. These fish are the whole resource. There’s no hatchery truck restocking a backcountry creek.
- Leave no trace. Pack it out, tread light, and walk the same line in and out.
Find your own, fish it quietly, and keep it to yourself. That’s the deal. Do it right and you’ll have wild trout and an empty drainage for a long time.