Which of the following fungi is known as aquatic mould?

Answer: Option A

Saproleginia is fungi that is known as aquatic mould.
Saprolegnia is a genus of water moulds often called cotton moulds because of the characteristic white or grey fibrous patches they form.
Saprolegnia filaments (hyphae) are long with rounded ends, containing the zoospores. Saprolegnia generally travels in colonies consisting of one or more species.