A surfer was bitten by a shark near Crescent Head, New South Wales, marking the fourth shark attack in the area within 48 hours. The 39-year-old man suffered minor cuts after the shark bit through his board on Tuesday morning. He is currently in hospital in stable condition. Earlier, three other shark attacks occurred in Sydney over the past two days. Following these incidents, police have closed all beaches in Sydney's northern region until further notice. NSW Superintendent Joseph McNulty said heavy rains have possibly created a "perfect storm environment" for shark attacks. Rain washes nutrients into the water, attracting sharks closer to shore. The latest attack happened near Point Plomer campground, around 450 km north of Sydney. Steve Pearce, chief executive of Surf Life Saving NSW, told ABC, "The surfer was very fortunate to not have sustained any serious injuries." He added, "We really strongly advocate that nobody swim or surf near river mouths because it's obviously an area where sharks congregate. If it's dirty water I'd think twice about going in there." Earlier attacks include a young surfer bitten at Dee Why Beach who escaped unharmed. However, a 27-year-old suffered "life-changing" injuries after an attack at Manly. On Sunday, a 12-year-old boy was critically injured at a Sydney Harbour beach. Authorities suspect bull sharks are responsible for these attacks. Bull sharks live in fresh and salt water and are considered one of the few shark species dangerous to people. The Australian Museum and the International Shark Attack File identify bull sharks as the third deadliest species. Last November, a bull shark killed a woman and seriously injured a man on a remote New South Wales beach. Despite these incidents, the chance of shark attacks remains very low. Due to recent poor water quality and visibility, police advise the public to avoid swimming in NSW harbours and rivers. Superintendent McNulty said, "I would recommend not swimming in the harbour or our other river systems across NSW at this time."