Which of the following retards the self purification of stream?

Given the detailed explanation, it is clear that:

- Higher temperatures can enhance microbial activity and thus increase the rate of oxidation, contributing to self-purification.
- Sunlight aids in photosynthesis, increasing dissolved oxygen levels, which helps in self-purification.
- Satisfying oxygen demand ensures that there is enough dissolved oxygen for oxidation processes, improving self-purification.

Thus, none of these factors retard the self-purification of streams. Therefore, the correct answer is:

D. None of the above

1.) Because sunlight helps in self purification by killing pathogens.
2.) Also streams will get self - purified in less time at higher temperature.
3.) If the oxygen demand is satisfied, then stream becomes purified.

how

For the self cleaning of stream min discharge is required.

Which of the following retards the self purification of stream?