Fishing the thin blue lines
Fishing in some thin blue lines can lead to catches of wild brown trout or native brook trout -- always worth the effort. (Jim Gronaw photo)

Back in the day, the days before the computer, there was a certain standardized process for finding good, little known or little fished angling adventures.

If you had a set of good, topographical maps, or some maps from ADC you were likely to find, with some diligent effort, some decent to good, or even very good fishing not too terribly far from home. Satellite imaging had not been developed yet and Google Maps were decades from happening.


Perhaps the best barometer for top drawer fishing was found in the confidence of a trusted friend who “knew the area” and was at least willing to share it with another trusted friend, perhaps you!

Fast forward to 2018, or even several years prior.

We have global mapping systems that are crazy good in terms of showing where and how to get places. Some of them are far and some are very near. And with the introduction of Google Maps and other computer options, most anglers and hunters can easily zoom in on a specific area, river, lake, or stream that they want to seek game and fish adventures. Much of this can be done on our smart phones or at our home computers prior to the trip.

Indications of roads, terrain and forest and foliage cover give us a pretty good indication of what to expect once we get there.

But one of the aspects of today’s computerized mapping systems is the input of the “thin, blue line” — an indication of small streams and tricklets that vein through our country side and wooded lands and beyond. Thin, blue lines (TBLs) can lead to outstanding catches or dead pools, banner days or dried up creek beds, fish-filled streams or polluted run-offs.

One thing for sure, TBLs have potential, even in this day and age of super-fast computerized info-gathering and instantaneous “big fish” communications, to offer some amazing fishing where few would think to look.

In all honesty, I have been doing my own version of TBL fishing for quite a number of years, even decades, to find untapped, micro-fisheries for smallmouth bass, trout, sunfish, and even carp or channel catfish. Most of them have names, but some do not.

I recently Google Mapped a TBL where I had, in years gone by, scored very high numbers of smallmouth bass and sunfish, with most of them being small. This was a water where my son Matt, at the tender age of 12, caught and released a 15-inch smallmouth bass more than 25 years ago.

The fish was at the base of a Sycamore tree root system that was on a sharp turn, creating a large eddy, at least it was large for this creeks’ standards.

On several spots on this trickle it would not have been too tough for a good high school long jumper to leap it in a single bound. Most of the shoreline was thickly overgrown with multifora rose and assorted evils like stinging nettle and poison ivy, making it necessary to wade in the water.

A three-foot deep hole was considered huge and it’s overall size was smaller than most living rooms. Years later, I would see a mounted, 17-inch smallmouth that came from the same water. Incredible fish for such a tiny, isolated and overlooked stream.

I can remember fishing a couple of different TBLs back in the 1990’s where the catch of the day was native brook trout, the only trout that is actually native to Maryland. I will not mention my guides name, as that may well give away this location, which, to this day, continues to support native brookies as well as some big, wild brown trout.

It took a considerable amount of hiking and stealthy approaches to coax those glorious natives and speckled browns to our hands for gazes and photos. Even at just 9 and 10 inches long we considered those native trout as “trophies.”

We never kept the wild or native trout as it was just a hoot to us knowing that they were still living there. Amazingly, on at least two mapping systems I have recently viewed, neither the bass nor the trout TBLs of those trips decades ago showed up with a name. Cool!


One of the other benefits of seeking the thin blue line is that you get a sense that you are creating your very own adventure even if other anglers have gone before you. In other words, it doesn’t have to be a totally virgin waterway, and almost never will be.

But it might be a run that has not been fished in many years or even decades. In the years gone by, anglers fished for food and many smaller waters were ignored, giving way to the bigger flows for size and volume of the catch. Finding your own hotspot, even today, is a distinct possibility, especially if you are willing to do a little mapping research and physical effort to find something that has been lost, maybe forgotten.

Some of the larger TBLs have names.

Others have small bridges that span them, thus providing some form of access. Many, however, are on private soil. Yet others have undergone major changes in both upstream development or, hopefully, lack of it.

Creeks with heavy canopies of trees and vegetation can provide cooler, more suitable water temperatures for a variety of freshwater species. Other, intricate systems are connected to current trout waters and may offer exciting opportunities both upstream and down. Still others offer a shot at 8 to 10 different species of fish within a single trip.

The Potomac and Susquehanna watersheds are loaded with a lifetime of “thin blue lines.” Discover a couple for yourself and enjoy your own adventure.

Smallmouth bass of varying sizes often reside in many "thin blue lines" that snake their way throughout central Maryland and southern Pennsylvania.
Smallmouth bass of varying sizes often reside in many "thin blue lines" that snake their way throughout central Maryland and southern Pennsylvania. (Jim Gronaw photo)