One of my wife’s cousins sent her a link to “How wolves change rivers”.  See https://www.youtube.com/watch?v=ysa5OBhXz-Q&feature=youtu.be.  At first I thought it was about how wolves move from one river valley to the next.  It really is about how wolves change a whole eco-system around a river, from the reintroduction of other species to less erosion of the riverbanks.
The five-minute video is about how the re-introduction of wolves into Yellowstone National Park reduced the deer that had over-browsed.  This in turn allowed plants to get bigger, including trees.  Bigger plants and trees provided food and shelter for more and more species including bears, beavers, and birds.
This led me to think about my previous column “Five simple steps to lower gas prices”.  As we build more and bigger highways, we need to salt them when they get icy.  As the weather warms, the saline solution goes into the ditches and drains.  This eventually makes its way into rivers.
California, among many other states, has a problem with excess salinity in water used by humans.  See “Desalination Can Address Major Threat Salt Poses to California’s Water Supplies” at http://www.caldesal.org/salinity-management/.  It doesn’t mention the effect of excess salinity on fish and other animals dependent on river water, but it does mention two effects that it has on humans.
“Salt buildup in agricultural soils and water sources has destroyed mighty civilizations in the past and, if left unmanaged, can do so readily again.”
“[Salt buildup eventually chokes] the root zone for plants and makes thousands of acres unfit for farming.”
The Colorado River furnishes water for irrigation and other uses for 40 million people.  Consumption is so great that the Colorado doesn’t reach the sea except in years of heavy rain.
This reminds me of Herodotus writing that the Persian army invading Greece was so huge that it drank rivers dry.
Most Americans have heard of the Cuyahoga River in Cleveland burning because of the pollution.  That happened after I left, but whenever I crossed it by streetcar or auto it was not a pretty site.  However, much of the heavy industry is no longer located in “The Flats”, and that which is doesn’t pollute as much as was done in the 40s and 50s.
The Hudson River was another tragedy.  Pete and Toshi Seeger and many others worked for years to get it cleaned up from PCBs.  The Hudson still has many problems including the effects from large amounts of water being withdrawn for cooling of a nuclear power plant.
The Mississippi River, Ol’ Man River, keeps rolling along and poisoning the Gulf of Mexico.  Agricultural runoff has created a dead zone in the Gulf.
The Columbia River may be one of the most dammed rivers because of its sharp average drop.  Damming a river has both benefits and drawbacks.  One of the benefits is hydroelectric power, possibly the cleanest and generally most reliable form of energy.  The drawback is that it limits the migration upriver of fish like salmon.  No salmon currently migrate to the upper half of the Columbia.
One of the most damaging effects on the Columbia River was the Hanford Nuclear site.  Water was taken out of the river for cooling, held for six hours for certain radio-active isotopes to decay, and then put back into the river still containing longer-lived isotopes.  Also much radioactivity is going into the groundwater.
“When the Yellow River runs clear” is the Chinese equivalent of “when pigs fly.”  The Yellow River is full of natural sediments that give it its name.  These sediments in turn cause heavy natural flooding that can take over one million lives.  People compound this problem by building levees.  If water breaks through then it cannot flow back into the main channel downstream.
However, several times breaking the levees has been used as a military strategy, one being in 1938 to stop the advancing Japanese army.  That flood took the lives of an unknown number of Japanese soldiers but also those of over a half-million Chinese.
The Danube in Europe is a very storied river and you can read more about it in Wikipedia, as well as about the other rivers that I mentioned.  We often refer to other rivers with a preceding article and sometimes a following “river”.  The Danube, at least in English, has no following “river”.  Maybe you can figure out its etymology from the Wikipedia article.
I haven’t researched what people have done to it, and so I can’t write about any pollution.  I will say that I didn’t find it “The Blue Danube” of the song, the Wikipedia pictures notwithstanding.  When I crossed it in both Vienna and Budapest, it looked brown to me.  Maybe I was in these cities after a heavy rain.
As for “How People Change Rivers”, Pete Seeger sang it well in the ‘60s’ and on: “When will we ever learn, when will we ever learn.”  I know, I know, he used “they” instead of “we”, but in the words of another immortal, Pogo, “We have met the enemy and he is us.”
You can find more of my thoughts at
http://magree.blogspot.com