Using numbers, graphs, and charts, scientists and academics routinely define the theoretically perfect stream. Riffle-to-pool ratios, frequency of meanders divided by stream width, the optimal mix of substrate, from pebbles to rocks to boulders, and more are used to see if a river is good enough as is or if it might need some improving. These calculations are normally done on a whiteboard, on a sheet of graph paper, or on a computer. I’ve seen many of the results, and 100 percent of the time, their descriptions are accurate, but at the same time perfectly wrong. The perfect trout stream no more exists in a math solution on a sheet of paper than the perfect ivory-billed woodpecker exists in some mothballed drawer at the Smithsonian Institution.
A few years back, I read an excellent breakdown of the perfect trout stream in one of the national bait-and-bullet magazines. I didn’t agree with all the findings, but it did make me think. The author interviewed a fisheries biologist who ran a company that improves and rehabilitates trout streams. The scientist provided the wonky details, and the author added the color that is missing from the raw math definitions used by most experts.
Here are a few of the interesting and thought-provoking takeaways from the piece that quantified the virtues of a perfect trout stream.
“The perfect trout stream will have an equal number of riffles and pools.” I don’t buy that for a second. Show me the riffles on Idaho’s Silver Creek or the pools on Montana’s Madison River. The Madison has been described as a 50-mile riffle with barely any pools to interrupt its flow. In my mind, both Silver Creek and the Madison are perfect left just the way they are.
“The perfect trout stream will have diverse benthic macro-invertebrate populations.” Maybe. Some of my favorite trout streams are at high elevations or have relatively fine substrates where BMI populations tend to be quite thin.
In these streams, a major component of trout food items consists of terrestrial insects, rather than aquatic bugs, and the trout are fat and happy. I’ll give this claim an 8.
“The perfect trout stream will have fish diversity.” Fish diversity only demonstrates that a stream has a diverse palette of habitat capable of being exploited by a variety of fishes. Sometimes fish diversity is a minus when managing a trout stream. California Trout (then California Trout Unlimited) poisoned the lower reach of Hat Creek to kill off a diverse population of native “trash” fish and repopulated the stream with rainbows and exotic brown trout. Over the next decade and a half, the trout population in Hat Creek exploded from 11 pounds per acre to 63 pounds per acre. For many years, Hat Creek was recognized as one of the top bucket-list fly-fishing destinations in the world. Hardly diverse, but widely recognized as near perfect.
“The perfect trout stream will have shallow riffles.” The reasoning is sound. Riffles are fast moving, so they tend to clean themselves of silt and sand and create lots of nooks and crannies in which various forms of fish food can thrive.
Even during periods of high water temperatures, riffles are oxygen-rich havens, because of the physical entrainment of bubbles caused by water crashing into boulders and stones. Finally, riffles are productive, because sunlight can penetrate their shallow waters and support the growth of nutritious algae on the river bed. A little algae goes a long way, but you don’t need acres of it. Seen hand in hand with claim number one (the perfect trout stream will have a 1:1 riffle-to-pool ratio), I understand it is true that shallow riffles are a bonus, but I certainly don’t consider long reaches them necessary for the perfect trout stream.
“The perfect trout stream will have structural diversity and varied substrate.” I’m totally on board with this one. It takes a variety of habitat types to support trout through their various life stages. There better be gravel to spawn in, cobbles for macroinvertebrates and fry to populate, and boulders, rocks, vegetation, and undercut banks to shelter grown fish. The Hat Creek project previously mentioned created one of the finest trout-fishing opportunities in the country. The same project also faces a long-term dilemma. A dam was constructed where Hat Creek enters Lake Britton to prevent nongame “trash” fish from reentering the creek after its poisoning. (Fish managers use the euphemism “chemical treatment” rather than “poisoning” to describe the eradication of undesired species.) Not only does the dam do a pretty good job of stopping the upstream migration of unwanted fish, it also blocks the downstream migration of sediment. As sediment builds up, the previously diversified streambed converts to one of little habitat complexity, which can crash a fishery. An example is Hat’s Carbon Reach.
“The perfect trout stream will have proper channel form.” Proper channel form reminds me of proper table etiquette or the proper way to ride a horse . . . everyone has their own definition of “proper.” River scientists have decided that proper channel form includes a generous degree of sinuosity, which rarely happens in any otherwise perfect trout stream cascading down an alpine slope. Proper channel form also states that for every foot of depth, the stream should be about 25 feet in width, the logic being that a river that is too shallow will get warm, and one that is too deep won’t allow an optimal amount of photosynthesis to take place. I know many perfect trout streams, but very few conform to the geeky prescription of “proper” channel form. I’ll give this one a 3.
“The perfect trout stream will have a temperature range of 52–66 degrees.” Give me a break. The perfect trout hatchery might exist entirely within these confines, but a perfect trout stream will proudly cross those gradients. One of the most productive trout streams in America is Montana’s Big Hole River. This is a river that sports winter anchor ice and summer water temperatures that regularly soar well into the 70s. Not only is the Big Hole incredibly productive, but it ranks among the top five most popular (perfect?) trout streams in the country. When taken by itself, water temperature is probably the single most important factor governing the productivity of a trout stream, but throw in influences such as complex river currents, depths, cover, oxygenating riffles, and vegetation, and the rigid confines of a temperature range relax considerably.
What is the perfect trout stream? Everyone probably has his or her own idea of what that might be. I’d love to hear your definition. I identified what I believe are the perfect trout streams, then looked for common denominators. Examples of my favorites include a tiny creek near Downieville and most high-elevation streams in the Sierra. In my opinion, the Kern River near Volcano Falls in the Golden Trout Wilderness ranks as the most perfect trout stream in California, perhaps in the world. Rock Creek and the upper Boulder River, both in Montana, are perfectly perfect in every regard. These rivers and streams are wildly different from one another in many ways, and after scratching the surface, it is easier to see the differences than the commonalities.
The one aspect that all these share, and it was an unexpected epiphany to me, is that none of these rivers are dammed, diverted, exceedingly pumped, or manipulated in any way. When left alone, there is nothing to fix. These waters come perfect right out of the clouds, the mountains, and the canyons. In most every way, Rock Creek is a hydrologic and biological twin of the Truckee, yet I find it many times more enjoyable to fish than my home water for reasons I can’t really put my finger on. In the attempt to define the parameters of a perfect trout stream, we somehow denigrate the streams. The more we attempt to make them better by dredging the silt, or adding tree stumps, boulders, riprap, and wire-wrapped gabions in an attempt to recreate or improve upon the natural state, or modifying the landscape with footbridge crossings and asphalt bike paths, the further we seem to move from the goal of finding the perfect trout stream. Maybe it is time that we reassess how to perfect the perfect trout stream and instead strive to be good stewards, rather than try to improve upon nature’s way.
