Increase in the BOD of water reservoir is due to

Options

A. Algae
B. Soil
C. Moss
D. Waste product

Answer

### Step-by-Step Solution:

1. **Understanding BOD**:
- Biological Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. It is an important indicator of water quality.

2. **Identifying Factors Affecting BOD**:
- BOD is influenced by the presence of organic matter in the water. The more organic matter present, the higher the BOD, as more oxygen is required for the decomposition process.

3. **Analyzing the Options**:
- **Option A: Algae** - While algae can contribute to oxygen levels, they do not directly increase BOD significantly.
- **Option B: Soil** - Soil can introduce some organic matter but is not a primary contributor to increased BOD in water reservoirs.
- **Option C: Mosses** - Similar to algae, mosses do not significantly contribute to BOD levels.
- **Option D: Waste Products** - Waste products, such as sewage and decaying organic matter, are the primary contributors to increased BOD levels in a water reservoir.

4. **Conclusion**:
- The increase in BOD of a water reservoir is primarily due to the presence of waste products. As the concentration of waste increases, the demand for oxygen by microorganisms also increases, leading to a higher BOD.

### Final Answer:
The increase in the BOD of a water reservoir is due to **D: the waste products**.

---