Read the following statements carefully and find the incorrect statements:
A. More than 1 percent impurities make domestic sewage unfit for human use.
B. Less BOD causes mortality of fish and other aquatic creatures.
C. Presence of large amounts of nutrients in water also causes excessive growth of planktonic algae, called an algal bloom.
D. Algai bloom causes deterioration of the water quality an decreases fish mortality.
E. Some bloom-forming algae are extremely toxic to human beings and animals.
F. Eichhornia crassipies is the world's most problematic aquatic weed.

Options

A. A, C , E and F
B. C , E and F
C. A, B and D
D. All are correct

Answer

To solve the question regarding the incorrect statements about domestic sewage and its effects on aquatic life, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement A**: "More than 1 percent impurities make domestic sewage unfit for human use."
- **Analysis**: This statement is incorrect. Domestic sewage becomes unfit for human use at a much lower threshold of impurities, typically around 0.1%. Therefore, this statement is false.

2. **Statement B**: "Less BOD causes mortality of fish and other aquatic creatures."
- **Analysis**: This statement is also incorrect. A lower Biochemical Oxygen Demand (BOD) indicates that there is less organic matter in the water, which means there is sufficient oxygen for aquatic life. High BOD, on the other hand, leads to decreased dissolved oxygen levels, which can cause fish mortality. Thus, this statement is false.

3. **Statement C**: "Presence of large amounts of nutrients in water also causes excessive growth of planktonic algae, called an algal bloom."
- **Analysis**: This statement is correct. High nutrient levels, particularly nitrogen and phosphorus, promote algal blooms in aquatic environments.

4. **Statement D**: "Algal bloom causes deterioration of the water quality and decreases fish mortality."
- **Analysis**: This statement is incorrect. Algal blooms actually deteriorate water quality and increase fish mortality due to reduced oxygen levels and toxins produced by some algae. Therefore, this statement is false.

5. **Statement E**: "Some bloom-forming algae are extremely toxic to human beings and animals."
- **Analysis**: This statement is correct. Certain types of algae can produce toxins that are harmful to both humans and animals.

6. **Statement F**: "Eichhornia crassipes is the world's most problematic aquatic weed."
- **Analysis**: This statement is correct. Eichhornia crassipes, commonly known as water hyacinth, is considered one of the most problematic aquatic weeds due to its rapid growth and negative impact on water bodies.

### Summary of Incorrect Statements:
- The incorrect statements are A, B, and D.

### Final Answer:
The incorrect statements are A, B, and D.

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