Eutrophication is often seen in

Options

A. deserts .
B. fresh water lakes.
C. ocean.
D. mountains.

Answer

### Step-by-Step Solution:

1. **Understanding Eutrophication**:
- Eutrophication is defined as the process of nutrient enrichment, particularly with nitrogen and phosphorus, in a water body. This leads to an increase in the growth of plants and algae.

2. **Identifying Causes**:
- The primary causes of eutrophication include the runoff of fertilizers, sewage, and other nutrient-rich substances into water bodies. This nutrient enrichment supports dense growth of algae, known as algal blooms.

3. **Effects of Eutrophication**:
- The algal blooms can block sunlight from reaching aquatic plants and, when the algae die, their decomposition consumes oxygen in the water. This depletion of oxygen can lead to the death of aquatic animals, creating a hypoxic environment.

4. **Where Eutrophication Occurs**:
- Eutrophication is commonly observed in freshwater lakes. This is because these lakes are often subject to contamination from sewage and agricultural runoff, which introduces excess nutrients into the water.

5. **Conclusion**:
- Based on the understanding of eutrophication and its causes, the correct answer to the question "Eutrophication is often seen in" is **freshwater lakes**.

### Final Answer:
Eutrophication is often seen in **freshwater lakes**.