Thermal Pollution: Causes and Effects to Water Quality and Ecosystems

When people consider types of water pollution, thermal pollution, and its effects are likely not the first thing that come to mind, but these changes to the environment can have devastating impact towards water quality and costs to habitats. Thermal pollution decreases water quality through any process which causes changes in ambient water temperature. Thermal pollution is often caused when an industry or human source takes in water from the environment, causes a change in water temperature, and returns it to the natural source. This simple use of heating or cooling water can have large effects to the oxygen levels in a body of water which impacts local ecosystems and the environment. This pollution can also affect plant life and side stream vegetation.

Causes of Thermal Pollution

1. Manufacturing and industrial plants using water as a cooling source for power. 
The largest source of thermal pollution is from production and manufacturing plants. Water is drawn to keep machines cool, and then returned at a higher temperature, which increases the temperature of a river, ocean, or body of water. This practice decreases the quality of water and can destroy habitats if it is not controlled. This can also affect vegetation surrounding the water edges which depend on a constant temperature.

Main sources of this type of pollution include Nuclear power plants, coal fired plants, industrial effluents, and hydroelectric power.

2. Deforestation
Trees, plants, and foliage provide shading and protection for lakes, ponds, and rivers from direct sunlight. Deforestation exposes these bodies of water directly to sunlight, which raises the temperature. This can also lead to higher concentrations of greenhouse gases which warms the surrounding areas.

3. Domestic Sewage
Sewage water which enters bodies of water with minimal or no treatment will have a higher organic temperature, and change water temperature. This can affects oxygen dissolved in receiving waters and can result in deaths of aquatic life.

4. Soil Erosion
Consistent erosion causes the temperature of water bodies to rise. Along with clouding waters, soil erosion will cause the temperature to increase and can prove threatening by increasing anaerobic conditions threatening oxygen levels.

5. Water runoff from paved surfaces
The temperature of water running over warm surfaces will increase, and this will also raise water temperatures when it enters sewer systems or any body of water.

6. Natural causes
Water temperature can also rise from natural sources such as volcanoes, and geothermal activity under water. This can have significant impacts on our environment.

Effects of Thermal Pollution

1. Decrease in dissolved oxygen levels
Warmer temperatures reduces level of dissolved oxygen in water. Warm water holds less oxygen than cold water. The surrounding habitat and ecosystems depend on a consistent level of oxygen, and changes to this can suffocate plants and animals. Algae will also thrive in warmer water and this further decreases the amount of oxygen available.

2. Increases level of toxins
Water which is warmed through industry and plants often is returned with toxins along with an increase in temperature.

3. Loss of biodiversity and ecological impacts
These changes to the environment can threaten or cause organisms to migrate. Organisms which can easily adapt to changes in water will also have an advantage over others that may be more sensitive. Water temperature can affect species differently, but sudden changes can result in mass killings of fish, insects, plants, or amphibians.

4. Interference in life
Activities of fish life including nest building, hatching, spawning, reproduction, and migration can all depend on water temperatures. Changes in water temperature can affect the the normal order and reproduction of species. Many species will migrate to more suitable environments after changes to temperature of habitat or interferences with ecosystems food chain.

Thermal Pollution has a devastating effect, but methods can be put in place to minimize damages and control temperatures. Many industrial facilities will use cooling towers, cooling ponds, Spray ponds, or create artificial lakes to address thermal pollution and manage water temperature. However, many will not monitor the damage and leave a harmful impact. 
As an individual, it is important to be aware of all forms of pollution and negative impacts we can have on our surroundings. Being informed helps enable use to have a positive impact, spread awareness, and hold industries to higher standards. We can also take steps to use less energy or alternate sources of energy to indirectly prevent thermal pollution.

Sources and further information:
Greentumble Editorial team. “What Is Thermal Pollution?” Greentumble - Together to Support Awareness & Conservation Activities, Greentumble , 6 May 2017,
Gour, Mrinal. “Environmental Studies.” Thermal Pollution - Causes, Effects and Control Measures of Thermal Pollution, Osmania University, 4 Nov. 2013,
Rinkesh. “Causes and Effects of Thermal Pollution.”Conserve Energy Future, 24 Dec. 2016,