Fishes in eutrophic lake is died due to

Options

A. Oxygen
B. Nutrient enrichment
C. ` CO_2`
D. None

Answer

**Step-by-Step Solution:**

1. **Understanding Eutrophication**: Eutrophication refers to the process where water bodies, such as lakes, become enriched with nutrients, particularly nitrogen and phosphorus. This often results from agricultural runoff, sewage discharge, and other human activities.

2. **Nutrient Enrichment**: In eutrophic lakes, the high levels of nutrients lead to excessive growth of microorganisms, particularly algae. This phenomenon is often referred to as algal bloom.

3. **Microorganism Growth**: As the algae and microorganisms proliferate, they consume a significant amount of oxygen in the water during the process of decomposition. This occurs when the algae die and are broken down by bacteria.

4. **Oxygen Depletion**: The increased microbial activity leads to a decrease in dissolved oxygen levels in the water. Oxygen is essential for the survival of aquatic life, including fish.

5. **Impact on Fish**: Fish and other aquatic organisms rely on dissolved oxygen in the water to survive. When the oxygen levels drop significantly (a condition known as hypoxia), fish cannot obtain enough oxygen to breathe, leading to suffocation.

6. **Conclusion**: The primary reason for fish deaths in eutrophic lakes is the low oxygen levels caused by the excessive growth of microorganisms that consume oxygen. Therefore, the correct answer to the question is that fish die due to low oxygen levels in eutrophic lakes.