Civilized Richness

This is a hard pill for most of us to swallow, but water polluted with human or animal waste is always more productive than pristine water. H. T. Odum, one of the world's leading ecologists, once wrote, "Polluted streams are possibly the areas of highest primary productivity on the planet." The Bow River in Alberta is one example. Above the city of Calgary the Bow is relatively infertile and can be easily blind-fished. Below the city, where the waste of over a million people enters the river, it is fertile beyond comparison in that part of the country, and the trout show the pickiness, reluctance to feed at certain parts of the day, and hesitance to come to the surface that are common among well-fed fish. Studies in Michigan and Pennsylvania have shown that removing domestic sewage can dramatically reduce the productivity of a trout stream, while adding it can make an infertile stream rich. The same goes for water that flows through agricultural land. Sewage and agricultural fertilizer are rich in phosphates and nitrates, and the lack of these nutrients often limits plant growth in streams, so when you add them to a stream you get the same effect as when you sprinkle 5-10-5 on your sweet corn in the spring. A study in Wisconsin found that runoff from one hectare of agricultural land puts 7.7 kilograms of nitrate per year into a trout stream. This beneficial effect walks a fine line because pollutants can also increase the biological oxygen demand of a stream, especially in hot weather, and too much organic material without cool water and a lot of riffled water can suffocate trout.

Rounded quartzite boulders tell you this stream is not rich, and the trout will behave accordingly â?? they'll be easy!

Weeds in the water always indicate higher productivity, and as a result more invertebrates for trout to feed on. Watercress and stonewort thrive in alkaline environments rich in carbonates, and long, thin, bright green strands of filamentous algae tell you either that the water is rich in carbonates or that sewage or agricultural effluent is present. In a stream that runs through a town or city, you'll often notice that the bottom of the river is clean above town, while below town the rocks have a coating of algae or long strands streaming from them. The water will be richer below town, as it is in the Bow, but you should be aware that not all rivers have the head of cool water to compensate for the increased oxygen demand during the summer.

You can predict the richness of surrounding trout streams by taking a shower in a nearby house or inspecting the owner's plumbing. (You thought it was bad enough that normal people ridiculed you when you walked around in trout streams with a butterfly net. Now you're going to be knocking on doors asking for a cup of vinegar and a look at the bathroom sink.) Calcium carbonate in the water is the same stuff that causes "lime" in your plumbing. If the local water supply contains a high concentration of carbonates, chances are the nearest trout stream does, too.

Tailwaters Are Usually Rich, Too

Tailwaters like the South Platte can be as rich or richer than spring creeks, and the banks usually show stability, with no sign of frequent flooding.

I lied when I told you that spring creeks are the richest trout environments in the world. They are the richest natural trout environments. As a class tailwaters are the richest trout streams in the world, and when you think of the waters fishermen dream to wade in, you have trouble leaving out the Henry's Fork, Madison, Bighorn, Missouri, Delaware, White, Green, South Platte, or Frying Pan. All of these rivers famous for their imposing trout and plentiful hatches are made rich by the still waters above them. Dams, if they release water from the bottom of the reservoir above them, as most of the famous ones do, stabilize both flow and temperature by being miserly with spring runoff and doling it out throughout the summer. Floods are reduced, temperature extremes are moderated, and growth is easier. Nutrients are concentrated in the impoundments behind dams. Trout also benefit in tailwaters because plankton is washed directly into the rivers and eaten by insects and crustaceans. Natural streams have little plankton because it's hard to maintain a population if you keep getting washed downstream, so invertebrate life in tailwaters enjoys a tremendous bonanza found in few natural environments.

How Valuable Is Rock Flipping?

You might be thinking I've left out the most obvious way of determining the richness of a river â?? picking up a couple of flat rocks and looking at the insects waddling madly to get away. Unless you're prepared to set up a seine, however, and trash a couple of square feet of stream bottom to get a representative sample, and then compare this sample to other streams, I don't think you will get a fair idea of richness from rock turning. You may miss the right part of the riffle and pick up rocks that are barren just by chance. You might be looking late in the season, when most of the larger insects have hatched and their offspring are too tiny to be noticed. Many of the insects in a river cannot be found by turning over rocks â?? you'll only find the clinging and crawling species and will miss the burrowers and swimmers. Sculpins, other forage fish, and crayfish are food chain supplements, ingredients that support big trout, but you'll seldom see them when you turn over rocks in the shallows unless you look at the place the rock was rather than what is clinging to it. Also these animals usually live in deeper water than you want to reach your arm into.

Looking at rocks helps you pick a nymph pattern, particularly in richer streams where the pattern choice may be important, and although it can give you a hint at a river's diversity, diversity is not as important as richness when it comes to working out a fishing strategy. Gauging the richness of a river is like "pre-stream reading": a way of looking at the river as a whole system before you start gazing at current patterns and rocks.