How does polluted water affect fish

It can make their bodies work harder, even when they are supposedly at rest. That also is energy no longer available to avoid predators, to find food and to mate. Instead, the animals use that extra energy to rid their bodies of the pollutants. Such chemicals can damage their cells and tissues or reprogram how their bodies respond to the environment.

So their bodies work to break down those contaminants. Then they pee the remains out. If fish respond this way when they are exposed to just one drug, what would they do when their water held a mix of them? After all, water downstream from treatment plants tends to host low levels of many such compounds. In fact, they now report, fish exposed to such a mix can use up to a third of their energy just to deal with those pollutants. The researchers captured bluegills in unpolluted waters near Lake Ontario.

Then they divided these fish into three groups. They caged some of them 50 meters feet downstream from a nearby water-treatment plant.

They caged another group in waters meters a half mile downstream of the plant. The last fish were caged in unpolluted local water, well away from the treatment plant. When nutrients wash into waterways through storm runoff, they deplete oxygen in the water that fish need to survive. Nitrogen and phosphorus typically enter streams and lakes from fertilizers, dog waste, and other sources.

Over time, these nutrients build up in the water and promote algae and water plant growth, and as they decay, they lower oxygen levels in the water. Algal blooms can be harmful to fish as they feed upon algae, toxins accumulate within the fish, and when a predator fish consumes that fish, they too are consuming higher toxin levels.

Pesticides and heavy metals that enter waterways can also harm or kill fish. Synthetic pesticides used for weed and bug control are toxic in even small amounts. Heavy metals created when fossil fuels are burned enter the atmosphere, eventually making their way into bodies of water. When a fish feeds on harmful algae, it ingests toxins that accumulate in its body and are passed on to other fish that eat them.

Synthetic pesticides, such as weed and bug killers, are toxic to fish in low concentrations resulting in fish mortality and a decline in fish populations. Some fish are more sensitive than others and die at lower concentrations. Pesticides enter fresh and marine waters when applied to a lawn or agriculture field, and excess is washed into the water when it rains, or if the spray drifts when applied.

Burning fossil fuels outputs heavy metals into the atmosphere which deposit into bodies of water. Fish feed on invertebrates that live in the water. Take away this food source and they either die from starvation or move to a new habitat. These invertebrates include waterborne insects; pesticides are toxic to them in low concentrations.

However, if the pesticide does not kill the insect, it is transferred when a fish eats it. Over time, pesticide builds up in the fish until it reaches a fatal level.

Sediment is another pollutant that kills invertebrates. A thick layer of silt can smother bottom-dwelling invertebrates.