We are all aware that standing water is dead water if no recycling process occurs to aerate and purify it. The important thing which makes rivers different from stagnant pools of standing water is that they represent a flow of water, meaning that the opportunity to revitalize what was once presumed to be a dead river will always be an option. There are precedents to illustrate that human intervention can bring a sick body of water to a healthy state again if enough desire exists to bring this about.
While human intervention can be said to be the main culprit in degrading the qualities of a natural body of water it has also succeeded in bringing many rivers and lakes back to life. By way of example, Lake Erie, one of the Great Lakes on the border of Canada and the U.S., was once thought to be a dead lake and many journal articles and television documentaries lamented the loss of this once valuable resource. It is a part of an eastward flow of water into Lake Ontario via Niagara Falls and on into the St. Lawrence River. It once had a thriving perch fishing industry and tourism was a significant contributor to the quality of life in the ports located on this lake.
There is no doubt that an accelerated natural aging process of the lake, termed eutrophication, was the direct result of human activity in a process whereby the addition of phosphorus into the fresh water system resulted in elevated levels of nutrients, a phenomenon known as cultural eutrophication. In the 1960's large algal blooms resulted in masses of decomposing algae which led to a reduction in the oxygen content of deeper areas of the lake. This in turn led to reduced fish stocks and dead fish washing up on bathing beaches. Lake Erie was a dead lake, to all intents and purposes.
In 1972 the U.S. and Canada signed the 1972 Great Lakes Water Quality Agreement. Over the twenty years following this, the amount of phosphorus loading was reduced by 60 percent. This naturally led to a reduction in the phosphorus content of the lake resulting in an 89 percent decline of alga. The accidental introduction of the zebra mussel, a filter feeder, coincidentally reduced much of the remaining algal content and improved water clarity and health substantially for a few years.
Notwithstanding that, problems arose because of drastic changes to the lake's ecology brought about by the zebra mussel, particularly with respect to the food web. Zebra mussels are considered a nuisance because their selective feeding promotes the proliferation of the Microcystis alga which had not previously dominated the lake's waters. The mussels also secrete a toxin which can damage the livers of the larval fish which feed on them. Their waste products also fertilize further growth of Microcystis.
The lake has become a laboratory for the exploration of methods to substantially improve the quality of the Great Lakes overall. There is continued monitoring of phosphorus loading on both sides of the border. The goals for Lake Erie will ultimately be met through research and continued management programs. Complete success thus far has eluded science but this is because the ecology of the lake is not yet fully understood. Nevertheless, the lake is far from dead today because of the application of human effort to bring it back to life.
Since rivers are constantly replenished from their source, the presence or absence of industry on the banks has a great effect on their ecology. The best example is probably represented by the Ruhr River in Germany, which joins with the Rhine River in Duisburg. Duisburg is Europe's largest inland port in the heart of industrial Germany. The industries that once lined the Ruhr River have disappeared over the last few decades and as a result that river is now so clean that it provides the entire region with drinking water.
During the last fifty years we have developed a conscience over our environment such that we now demand that industrial pollution be abated as well as it can be and that the indiscriminate dumping of industrial and agricultural waste be outlawed and runoff curtailed. To that end the condition of many of the once most heavily polluted rivers and lakes the developed world over have actually improved during this time. The future will one day see industry recycling or properly disposing all of its waste products, cleaning its stack emissions before they enter the air, and manufacturing and processing goods and products transparently while we enjoy a healthy lifestyle on the shores of clean beaches and swimming in translucent lake water alive with sport fish. That is not a dream.