A man has been arrested for allegedly raping a woman, whom he had befriended on a social networking site, in a boat in the middle of the Ganga river near Kolkata's Prinsep Ghat, police said on Sunday.

He was apprehended from Behala on Saturday night and produced before a court on Sunday, they said.

The incident took place in March this year, following which the accused allegedly blackmailed her on a few occasions and extorted money from the woman, a police officer said.