Large scale death of fishes occur in

Options

A. Saline lake
B. Oligotrophic lake
C. Eutrophic lake
D. Shallow lake

Answer

To solve the question regarding the large-scale death of fishes, we need to analyze the different types of lakes mentioned in the options and understand the concept of eutrophication.

### Step-by-Step Solution:

1. **Understand the options**: The options provided are saline lake, oligotrophic lake, eutrophic lake, and shallow lake. We need to determine which type of lake is associated with large-scale fish deaths.

2. **Define Eutrophication**: Eutrophication is the process of nutrient enrichment in a body of water, primarily due to an increase in nitrogen and phosphorus. This process can occur naturally over time but can be accelerated by human activities such as agricultural runoff and sewage discharge.

3. **Effects of Eutrophication**: The increase in nutrients leads to excessive growth of algae, known as algal blooms. These blooms can cover the surface of the water, blocking sunlight and disrupting the aquatic ecosystem.

4. **Dissolved Oxygen Depletion**: As algae die and decompose, the decomposition process consumes a significant amount of dissolved oxygen in the water. This decrease in dissolved oxygen levels can lead to hypoxic conditions (low oxygen), which are detrimental to fish and other aquatic life.

5. **Conclusion**: Given that eutrophication leads to a decrease in dissolved oxygen due to increased nutrient levels and algal blooms, it is clear that large-scale fish deaths are most likely to occur in eutrophic lakes.

6. **Final Answer**: Therefore, the correct answer to the question "Large scale death of fishes occur in" is **eutrophic lake**.