harmful symptoms. More than one-third of the shellfish-growing waters of the United States
are adversely affected by coastal pollution.
Thermal Water Pollution
Thermal pollutionis anything that causes water temperatures to rise or fall (Figure
21.21). For example, power plants and other industries often use water to cool equipment.
Once the water absorbs heat from a power plant or industry, the heated water is returned
to the natural environment at a higher temperature. Cold water pollution can be observed
when very cold water is released from reservoirs.
Figure 21.21: The Macquarie perch is now extinct in most of its upland river habitats
partially due to thermal pollution by dams. ( 7 )
Why would changing water temperature harm the environment? Fish and other aquatic
organisms are often vulnerable to even small temperature changes. Heated water kills fish
and other organisms by decreasing oxygen supply in the water. Frigid water has a severe
effect on fish (particularly eggs and larvae), macro invertebrates and river productivity.
Lesson Summary
- Industrial, agricultural, and municipal sources produce harmful water pollutants such
as toxic chemicals, radiological agents, and animal wastes. Thousands of people die
from waterborne diseases every year.
Review Questions
- What do the initials ’EPA’ stand for?
- What is runoff and why is it a problem?