It could be a childhood trauma. Maybe he had a near - drowning experience when he was young that left a deep mark on his psyche.
It could be an inherited fear. Given his family history and the mysteries surrounding his parents, there might be some genetic or family - related factor that causes him to be afraid of water.
At first, Snape might be dismissive. He has a reputation for being harsh, so he could act like Harry's fear of water is a sign of weakness. However, as time goes on and he realizes the depth of the fear, he may change his attitude and, in his own unique way, try to assist Harry in facing it.
Snape might initially be surprised. He could then use this knowledge in a rather Snape - like way, perhaps to gain an advantage in his complex relationship with Harry. Maybe he'd be a bit more guarded in his interactions with Harry, or he could even try to subtly help Harry overcome his fear while still maintaining his tough exterior.
Snape might be initially shocked. He has his own preconceived notions about Harry, and this revelation could completely change his view. He might struggle to accept it at first, given his traditional and somewhat rigid personality.
The significance could be that it changes the power dynamic between them. Harry has always been a bit in the dark about Snape, but now Snape has a piece of information about Harry. This could lead to Snape having more influence over Harry, or it could also lead to Snape having a newfound sense of responsibility towards Harry, especially if the fear is something that could put Harry in danger.
The impact would be significant. Harry has always had a complicated relationship with Snape. When Snape discovers Harry is gay, it could shatter some of the pre - existing barriers between them. Snape, who has his own secrets and pain, might find a new connection with Harry. This could lead to a transformation in their relationship. Harry may start to trust Snape more, and Snape could finally let go of some of his old grudges against Harry. They could end up having a more positive and supportive relationship, which would be a huge change from their often - hostile past interactions.
In some fanfics, Harry's fear is depicted through his thoughts. He constantly has internal monologues about Snape, like wondering what Snape is really thinking or if Snape is plotting something against him. His dreams might also be affected, having nightmares about Snape and his actions.
He'd probably be annoyed. Snape is a serious wizard and he might think fanfiction is a silly Muggle - influenced concept.
Snape might be initially shocked but then try to hide his concern. He's a complex character. He could act indifferent in public but secretly start to gather information about who is behind the abuse. He might also start to keep a closer eye on Harry without the boy realizing it.
Snape could be very cold at first, but then his natural instinct as a healer (since he is quite good at potions which are often used for healing) might take over. He might give Harry a potion to ease the pain and start to patch him up. All the while, he would probably be scolding Harry for being so reckless and getting into a situation where he got injured.
Well, it could lead to a major turning point. Snape might be shocked and try to help Harry get the support he needs.