A lake which is rich in organic waste may result in

Options

A. Increased population of aquatic organisms due to minerals
B. drying of the lake due to algal bloom
C. increased population of fish due to lots of nutrients
D. mortality of fish due to lack of oxygen

Answer

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks about the consequences of a lake being rich in organic waste. Organic waste can come from various sources such as sewage, agricultural runoff, and decaying plant material.

2. **Identifying the Effects of Organic Waste**: When a lake has a high concentration of organic waste, it leads to an increase in nutrients in the water, particularly nitrogen and phosphorus. This nutrient enrichment can trigger a phenomenon known as algal bloom.

3. **Understanding Algal Bloom**: Algal blooms occur when there is an excessive growth of algae due to the high nutrient levels. These blooms can cover the surface of the water, blocking sunlight from reaching underwater plants.

4. **Consequences of Algal Bloom**: The lack of sunlight due to the algal bloom can cause underwater plants to die. When these plants die, they decompose, which is facilitated by microorganisms.

5. **Microbial Activity and Oxygen Consumption**: The decomposition process carried out by microbes consumes dissolved oxygen in the water. As the organic matter is broken down, the demand for oxygen increases, leading to a depletion of dissolved oxygen levels in the lake.

6. **Impact on Fish Population**: Fish and other aquatic organisms rely on dissolved oxygen for survival. As the oxygen levels drop due to microbial activity, fish begin to experience stress and can ultimately die from lack of oxygen.

7. **Evaluating the Options**:
- **Option A**: Increased population of aquatic organisms due to minerals - Incorrect, as organic waste does not increase mineral levels.
- **Option B**: Drying of the lake due to algal bloom - Incorrect, as algal blooms do not dry out the lake.
- **Option C**: Increased population of fish due to lots of nutrients - Incorrect, as the nutrients lead to oxygen depletion rather than an increase in fish.
- **Option D**: Mortality of fish due to lack of oxygen - Correct, as the depletion of oxygen from microbial activity leads to fish deaths.

8. **Conclusion**: The correct answer is **Option D: Mortality of fish due to lack of oxygen**.