Question

Polluted waters do not contain

• A. Water hyacinth
• B. $Cyanobacteria$
• C. Stonefly larvae
• D. Sewage fungus

Answer 1

The correct option is C Stonefly larvae

Stonefly larvae
Larvae of stoneflies won't be found in polluted water.
Stoneflies are sensitive to contaminated water and therefore they do not survive in it.
Stoneflies are generally found in clean and unpolluted water.
The presence of stoneflies is an indicator of better water quality.

Sewage fungus
Sewage fungus is usually found in polluted water.

Water hyacinth
Water hyacinth is a free-floating aquatic plant native to America. Water hyacinth is the common name for $Eichhorniacrassipes$.
Also, it is a major freshwater weed and is regarded as the most troublesome aquatic plant. It is also found in polluted water.

$Cyanobacteria$
$Cyanobacteria$ is a blue-green algae, known for nitrogen fixation.
These grow rapidly under contaminated water.

Final answer
(A) Stonefly larvae