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River pollution is obvious when you can visibly see dead fish floating at the top of the water or gathering along the sides of the river bank. Polluted water also smells really bad and you can usually smell the stench of the water.
Fertilizers are a known cause to river pollution. This is because fertilizers have a high concentration of nitrates and phosphates and when it rains, the run off water that drains into the rivers, brings the fertilizers with it and all of the algae growth too. Algae grows rapidly and it uses up all of the oxygen in the water, which is known to kill many animals.
Industrial waste being dumped into the water is also responsible for river pollution too. Many of these pollutants can include cyanide, zinc, lead, and mercury. Obviously, things like this getting dumped into the water will kill the fish and the living organisms in the water.
Oil pollutes the rivers also when it is spilled or when it enters the water. When oil has entered a body of water, it is visible on top of the water because it creates film over the top of the water. Oil contaminates animals too.
Warm water is another big factor for river pollution and that is because when warm waters enter into a body of fresh water it can send the life in the area into shock. Fish can swim to another location, but usually plant life dies because it cannot move. Warm water enters rivers from being runoff from rain and draining over the concrete into the rivers. Some companies use water to cool off hot machinery and dump the hot water back into the rivers, not thinking of the consequences this can have with the wildlife.
There are many things that cause river pollution. Awareness is key to fixing the problems.