Eutrophication of water bodies is caused by excessive discharge of nutrients.

Eutrophication is a process in which water bodies, such as lakes, rivers, and oceans, become enriched with excessive nutrients, leading to an overgrowth of plant life, particularly algae. This excessive growth of algae disrupts the balance of the ecosystem and can have detrimental effects on aquatic life and water quality.

Causes of Eutrophication:
Eutrophication is primarily caused by the excessive discharge of nutrients, particularly nitrogen and phosphorus, into water bodies. These nutrients can come from both natural and anthropogenic sources.

Natural sources:
- Weathering and erosion of rocks and soil, which release nutrients into water bodies.
- Decomposition of dead plants and animals, which also release nutrients.

Anthropogenic sources:
- Agricultural activities: The use of fertilizers in farming leads to the runoff of excess nutrients into nearby water bodies. This runoff can occur during rainfall, irrigation, or improper storage and handling of fertilizers.
- Wastewater discharge: The discharge of untreated or poorly treated sewage and industrial wastewater into water bodies can contain high levels of nutrients.
- Urban runoff: Stormwater runoff from urban areas can carry nutrients from lawns, gardens, and streets into water bodies.
- Deforestation: The removal of vegetation increases soil erosion, which can transport nutrients into water bodies.
- Aquaculture: Fish farming and aquaculture operations can release excess nutrients into surrounding water bodies.

Effects of Eutrophication:
- Algal blooms: Excessive nutrients in the water promote the growth of algae, resulting in algal blooms. These blooms can lead to a decrease in water clarity, as well as the formation of harmful algal toxins.
- Oxygen depletion: When the algae die and decompose, the process consumes oxygen, leading to oxygen depletion in the water. This can suffocate fish and other aquatic organisms.
- Disruption of the food chain: Eutrophication can alter the balance of the food chain, as excessive algae growth can outcompete other aquatic plants and decrease the availability of food for herbivores and higher trophic levels.
- Loss of biodiversity: Eutrophication can lead to the loss of sensitive species that cannot tolerate the changes in water quality and habitat conditions.
- Water quality degradation: Eutrophication can result in foul odors, taste, and appearance of the water, making it unsuitable for drinking, swimming, and other recreational activities.

Prevention and control measures:
- Implementing proper nutrient management practices in agriculture to reduce fertilizer runoff.
- Treating wastewater to remove nutrients before discharging into water bodies.
- Implementing best management practices for stormwater management in urban areas.
- Protecting and restoring riparian zones and wetlands, which act as natural filters for nutrients.
- Enhancing public awareness and education on the impacts of nutrient pollution and the importance of responsible nutrient management.

In conclusion, excessive discharge of nutrients, particularly nitrogen and phosphorus, is the main cause of eutrophication in water bodies. Understanding the sources and effects of nutrient pollution is crucial in implementing effective prevention and control measures to protect and restore water quality.