Why do you think that the salmon are not returning to the Columbia River?
Rivers
Rivers play a very important in nature and in the lives of humans, plants and animals. They play an important part in the hydrological cycle - when it rains over land, or snow or glaciers melt, some of the water flows into streams then rivers before finally ending up in the sea. Then water in the sea evaporates, the clouds move over the land, and the water falls as rain or snow and the cycle starts all over again. Rivers help shape our landscape, creating waterfalls, canyons and deltas which are rich in wildlife.
Rivers are home for many creatures, from fish to crustaceans to insects and spiders, water voles, water birds and alligators. Beavers create dams on smaller rivers to create pools. As well as the fish living year-round in the rivers, some fish such as salmon use rivers to spawn but live in the sea at other times. Manatees and sea lions and other larger creatures live in the rivers nearer the coast. Many animals, wild and domesticated, come down to the river to drink, where predators lay in wait for them.
Rivers have long been of use to humans as transport systems, sources of water for drinking, washing and irrigation, and sources of food. Then mankind began to harness them for power by building small dams and watermills. They were also used to transport more and more goods, from logs to the local mill to international goods from major upriver ports such as Portland, Oregon. Larger dams were created for hydroelectric power. The larger the project, the greater the disruption to people and wildlife living in the area. In some cases, attempts have been made to alleviate the problem, such as fish ladders for returning salmon, and evening out the flow better so fish are not stranded in pools or left completely dry. We also extract a great deal of water from either the rivers or aquifers for our cities, so that some rivers dry up completely.
Rivers have always carried away some silt and some metals and minerals from the surrounding land - for example, small nuggets of gold from upriver deposits. These days, however, they may carry a lot more:
- soil that has eroded from upstream lands due to logging and clearing
- silt and chemicals from mining operations (for example mercury and arsenic)
- fertilizer and pesticide run-off from agricultural land
- all sorts of chemicals and rubbish and sewage (with various degrees of treatment) from factories and homes
- air-born pollutants that have been washed out by rain
The fertilizer and some other run-offs can cause algal blooms which use up all the oxygen in the river causing fish to die. This can continue miles out to sea, for example in the Gulf of Mexico off the Mississippi. Toxic chemicals can kill or damage fish and other creatures, killing them off entirely or making them unfit for our consumption. Many of America's rivers have mercury advisories, for example.
We use larger navigable rivers as major transport systems, sometimes for international trade. All kinds of wastes from the ships pollute the waters, including oil spills. Invasive species arrive in the ballast tanks of international ships and are accidentally or deliberately discharged into the river. Others are bought in pet shops but are later discarded in rivers. These species can play havoc on the local ecosystem, sometimes destroying populations of sport or food fish, or clogging up machinery or waterways. Rivers may be used to extract water for cooling, which is then discharged back into the river raising its temperature. Pleasure boats also pollute rivers. The sounds from boats create noise pollution both in the water and above. We also fish in rivers both for food and for sport, and farm fish and crustaceans.
Rivers can pass not only through more than one region, county or state, but also through one or more country (for example, the Danube). This can lead to disputes between those upstream and those downstream if those upstream take too much water, or dam the river, or create too much pollution. Those either side of a river may also dispute where the boundary is (particularly if the river's course or sand or mud flats shift over time), and who is entitled to what water and fish.
Columbia River
The Columbia River (map and further information) in America's Pacific North West has been in the news quite often of late for various problems:
As you can see, there are many different factors affecting the health and suitability of the river for salmon, plus salmon spend much of their lives at sea where there are many dangers. So, it is not surprising that it is not as obvious as you might think why the salmon are not returning in their expected numbers.
Salmon Fishing Halted on Columbia River
Sport fishing for salmon, steelhead trout and shad has been suspended on the Columbia River because of a mysterious collapse in the population of salmon. Some commercial fishing of hatchery fish has also been stopped. Only one thousandth of the expected number of chinook salmon have returned to the Bonneville Dam east of Portland so far. The loss of sport fishing affects the local economies.
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