In addition, smaller animals that live and feed along this biologically vital corridor may include birds (like the ring-necked pheasant, grouse, geese, falcons, great blue herons, hummingbirds and warblers), small mammals (such as longtail weasel and striped skunk), reptiles (garter snake and the western painted turtle), and amphibians (red-legged frog and the Pacific giant salamander). The flora and fauna often include many threatened, endangered, or sensitive species, among which could be the bald eagle, peregrine falcon, and kit fox (The Columbia River Basin watershed and its ecosystems 2005). The plant life along the river can also has an effect on the health of the species living in the river by maintaining the health of the river by influencing the amount and kind of sediment in the river. The vegetation along the side of the river achieves this by anchoring soil, catching silt, filtering out pollutants, and absorbing nitrogen and phosphorus. This vegetation also provides shade to cool the water and so makes a habitat for insects and their predators (The Columbia River Basin watershed and its ecosystems 2005).

When there is too much sedimentation, which may occur when vegetation along riverbanks is removed by flooding or any other means, the river can become obscured. This occurs as sediment washes back into the water to cause turbidity, meaning that the sediment is stirred up and suspended in water. A river in this condition can impair the respiration of fish or other aquatic organisms. Such conditions can also cause sediment to cover gravel used for fish-spawning, raise the temperature of the water, and bury submerged plants (The Columbia River Basin watershed and its ecosystems 2005). This is the situation along much of the Snake River, some of it caused or exacerbated by the damming of the river. However, it is not clear if breaching the dams, as has been suggested, would be sufficient to alter the situation significantly given that breaching the dams would change the sedimentation but perhaps add to the turbidity.

Changes to the River

Many of the hydroelectric projects along the river alter the balance and can contribute to the sedimentation process. It is really the dams built for this purpose that cause the problem, and this includes dams built for other reasons, of which there are many. Specific ecosystem impacts are possible and are influenced by several variables, as follows:

the size and flow rate of the river or tributary where the project is located, the climatic and habitat conditions that are current, the type, size, design, and operation of the project, and whether cumulative impacts occur because the project is located upstream or downstream of other projects.

Dams create reservoirs or lakes, and these can significantly slow the rate at which water moves downstream. Because surface temperatures tend to become warmer as the slower moving or "slack," water absorbs heat from the sun, this can affect the nearby ecosystem. At the same time, the colder water sinks to the bottom because it has a higher density, and this in turn causes a layering effect called stratification, with the bottom layer the coldest and the top layer the warmest. There is also an ecosystem effect because the colder water that sinks toward the bottom contains reduced oxygen levels, and when water is released from the colder, oxygen-depleted depths, downstream habitat conditions change because of the reduced oxygen level in the water (How a hydroelectric project can affect a river 2005).

A related problem is cased by the accumulation of sediments, which are fine organic and inorganic materials that are typically suspended in the water but that can collect behind a dam because the dam itself is a physical barrier. Man-made and natural erosion of lands adjacent to a reservoir may cause sediment build-up behind a dam. The ecosystem can then be affected by the fact that 1) downstream habitat conditions can decline because these sediments no longer provide important organic and inorganic nutrients; and 2) because where sediment builds up behind a dam, "nutrient loading" can cause the supply of oxygen to become depleted because more nutrients are now available so that more organisms populate the area to consume the nutrients, using more oxygen. Gravel can be trapped behind a dam in the same way as sediment, and this can affect the ecosystem if there is a movement of gravel downstream (How a hydroelectric project can affect a river 2005).

According to a study conducted in 1991 by the U.S. Geological Survey, the water and sediment in the Snake River contains contaminants, found in streambed sediment and aquatic biota tissue. In 1992, fourteen sites in the upper Snake River Basin in Idaho and western Wyoming were analyzed, and mercury was identified as a contaminant in aquatic biota, representing contamination from natural or anthropogenic sources. Mercury enters the system from natural sources, including through the weathering of minerals and rocks. It also comes from human activities associated with mining,

Cinnabar is the most common natural source, and this is a mineral ore comprising mercury and sulfur. In streams, mercury occurs at higher concentrations in bed sentiment and biota than in the surrounding water. Microorganisms can synthesize inorganic mercury compounds into methylmercury, which is both the most bioavailable form of mercury and the most toxic form because concentrations accumulate in organisms and are then magnified in the food chain. Mercury is also a known mutagen and a carcinogen, capable of adversely affecting reproduction, growth and development, behavior, and the metabolism of the organism. The highest concentration of mercury was found in northern squawfish from the Columbia River Basin, thought to be caused by the presence of extensive natural cinnabar deposits and to mercury from mining in the basin. The elevated levels of mercury raise concerns because of the direct threat to human health from ingestion of these fish (USGS 2004).
Also of concern are the effects of the various dams and hydroelectric plants on the transport of salmon in the Snake River, and this has been assessed from time to time by the U.S. Army Corps of Engineers. The Corps studied the movement of sediment in the Snake River system and determined that Lower Granite Lake captures a current average annual sediment load of 3 to 4 million cubic yards per year carried by the Snake River due to basin runoff, with about 80% of this sediment inflow coming from the Snake River, while about 20% is from the Clearwater River. The report states that breaching of the four lower Snake River dams would allow the annual sediment load of 3 to 4 million cubic yards (2.3 to 3.1 million cubic meters) to be carried downstream to Lake Wallula, itself created by McNary Dam, which is the first dam downstream on the Columbia from the Snake River confluence. It is also estimated that approximately 100 to 150 million cubic yards of sediment have accumulated behind the four lower Snake River dams, and approximately 50% of this previously deposited sediment is likely to erode and move downstream within the first few years following dam breaching, particularly during peak flow periods. The remainder of the sediments not eroded within the first few years of dam breaching would then be subject to long-term erosion by wind and precipitation, and these might also in time be transported downstream to Lake Wallula. Potential deposition patterns have been projected, though future deposition patterns are difficult to predict due to the numerous variable factors involved, including the long-term unpredictability of seasonal flows, uncertain land use practices, and uncertainties of weather erosion due to precipitation and wind action. The Corps states that potential depth of sediment deposition in Lake Wallula is not likely to present navigation problems, but that future proactive measures to protect irrigation water intakes from sedimentation effects might be necessary in the area (Sediment transport analysis 1999, p. 1).

Conclusion

The Snake River is part of the Columbia River system, joining the Columbia in Idaho and crossing the Tetons and Yellowstone both. For much of its history, the Snake River was only visited by human populations, for the weather was too cold for habitation until recent times, hen modern houses can offer protection that earlier structures could not. The river is home to a variety of river life both plant and animal. The environment along the river includes game animals, birds, and the like as well as various forms of tree and grass. The viability of the entire system could be tested by changes in the river, some of which have been taking place because of numerous dams along the route of the river and the changes that these bring to the ecosystem.