Generally, trout streams are classified as freestone trout streams, taiilwaters and spring creeks. Of course, there are streams that have various combinations of spring creek water, tailwaters and freestone stream water, In this case, we are only covering freestone streams.
A freestone trout stream is born at the top of a mountain as drops of rainwater and a melting snow pack or snowflakes. As gravity forces these droplets of water to seep through the crevices of rocks, soil and organic matter, they combine into small trickles of water. These trickles eventually collide and become larger and larger. They form tiny streams. These tiny streams eventually join other tiny steams to form larger ones. These little streams are made larger along the way by many other trickles of water and eventually become large enough to have a name and be shown on a map. Often, these small streams are the headwaters of what will become a large freestone stream or river.
Generally, water in the headwater streams is at a higher elevation than the main stream. At some point, if not its entire length, most headwaters fall through steep gradients and rapidly flow downhill. As the stream reaches the lower elevations the gradients become less and the flow of the water decreases accordingly. As more and more water collects, the stream become wider and wider. The water in the larger streams slows down as it moves through the flatter terrain of the valley.
As it reaches the low elevations of the valley and the flows decrease due to the increased volume of water, the temperature increases. Eventually the water will become too warm to support trout and other warm water species of fish such as smallmouth bass start showing up The slower, moving water will not hold as much dissolved oxygen as the fast moving headwaters. This too becomes an important factor in the stream’s ability to support trout.
Depending upon the rocks, sand, gravel, and organic material (such as leaves and vegetation) the
water passes through as it flows downhill, the pH will usually increase. The pH of the headwater streams varies from region to region, depending on the composition of the soil and rocks. Rain forest type terrain, such as is found in the Appalachian Mountains and the Pacific, provides the water a different chemical composition than the more barren slopes of the Rocky Mountains, for example. The pH of the water also changes from the headwaters to the foothills.
The different pH values of the water, from its origin in the mountains to the larger streams or river in the valleys, supports different groups of aquatic insects. The water temperature is generally higher in the lower sections of the stream and this can also be a factor that affects trout in that it changes the insect population.
The speed of the water is also a big factor in determining which aquatic insects exist. Insects found in the fast flowing pocket water of the headwaters may be quite different from those found in the slower moving water found at the lower elevations.
Because the water is usually fast moving pocket water, mayflies found in the headwaters are usually clingers. Caddisflies are not very plentiful in these waters because of the acidic level of the water and consequent low algae levels.
Many species of stoneflies are in their prime habitat in the highly oxygenated water. This water, which is usually slightly acidic, will not support plant life such as algae. The aquatic insects must rely on other source of food. When the stream becomes the “run, pool, riffle” type of stream, normally found in lower elevation trout streams, the pH is generally higher and the water begins to support more species of aquatic insects that eat algae.
The stream’s volume of water and rate of flow is strictly dependant upon Mother Nature. The amount of water in the stream can vary drastically with the seasons of the year. Heavy rainfall that usually occurs in the spring months makes the freestone streams large and turbulent and sometimes flood beyond their normal banks. In the late summer and fall months of the year, most freestone streams reach their lowest levels. Sometimes the flow can become so slow and the dissolved oxygen levels so low that it become tough for trout to survive. This is especially true in the lower sections of the streams in the foothills.
Copyright James Marsh 2013