First we will take you through the three main influences on streams for salmon: water quality, water quantity, and physical structure!
Temperature: The temperature of a stream for a salmon is critical. Although salmon can survive a range between forty-five degrees Fahrenheit and seventy-seven degrees Fahrenheit, the preferred temperature for salmon is a range of fifty-five degrees Fahrenheit to sixty degrees Fahrenheit. They are very sensitive to the stream's change in water temperature. In the summer months, cool, deep pools are needed since the surface temperatures rise. Logs and logjams provide shade and colder water in smaller streams. An undercut bank and overhanging vegetation provide cool shelter in larger rivers like the Kenai River.
Dissolved oxygen: A healthy salmon population needs a sufficient amount of dissolved oxygen in the stream. Pollution, such as unproperly treated sewage, can increase temperature and decrease oxygen levels in the stream. Streams that have more aquatic plants have more oxygen.
pH: Streams should not be too acidic or basic. Salmon survive best in neutral waters. Large variations create an unstable aquatic system.
Turbidity: Turbidity, or water clarity, measures the amount of silt floating around in the water. High turbidity can increase water temperature and can reduce oxygen. When the silt settles, it can cover spawning sites and reduce oxygen to the developing salmon. The amount of silt in the Kenai River increases after heavy rains.
For a salmon stream, the amount of water that flows into the stream is important. When there is too much flowing water, the juvenile fish will be flushed downstream. High flows can make rolling boulders, logs and stumps change salmon habitat by scraping the gravel on the streambed. When there is too little water, it makes the riffles impassable and it also makes the stream have a lower oxygen content. Salmon in stream migration can be affected by low water flows.
The structure refers to the physical features in the stream such as pools, riffles, channels and barriers. Pools that have deep water give salmon shade, and protection. Riffles provide the stream with oxygen. As the water flows over the stones in the riffles, oxygen mixes into the stream. Aquatic insects, an important source of food for salmon, live among the riffles. The natural uneven edges of the banks can slow down fast moving waters, and give the juvenile salmon protection. The channels of the streams are important to salmon because during floods, the salmon can retreat into the slower moving waters.