A surfer has been bitten by a shark, the fourth attack along Australia's New South Wales (NSW) coastline in under 48 hours. The 39-year-old man sustained a wound to his chest after a shark bit his board on the Mid North Coast on Tuesday morning, police said. He has been released from hospital.

The incident follows three other attacks in Sydney over the past two days, leading authorities to close all beaches in Sydney's northern area until further notice. The attacks coincide with heavy rainfall, which may have created a 'perfect storm environment' for shark incidents. Rain can wash nutrients into the water, potentially drawing sharks closer to shore.

The latest attack occurred near the Point Plomer campground, approximately 450km north of Sydney. Steve Pearce, Chief Executive of Surf Life Saving NSW, noted that the surfer was fortunate to avoid serious injuries. He emphasized the risks of swimming or surfing near river mouths, as these are areas where sharks tend to congregate.

In the preceding 48 hours, a young surfer narrowly escaped an attack at Dee Why Beach while another incident at Manly Beach left a 27-year-old with serious injuries. Earlier on Sunday, a 12-year-old boy was critically injured at a popular beach in Sydney Harbour.

Experts believe bull sharks are involved in most recent attacks. Bull sharks, known to inhabit both fresh and saltwater, are considered one of the few species that pose a danger to humans and are categorized as the third deadliest shark species by the International Shark Attack File.

Despite Australia's reputation as a shark attack hotspot, the likelihood of an attack remains very low. However, the recent occurrences have been highly unusual, prompting police to advise the public to avoid waterways in NSW due to reduced water quality and visibility. Again highlighting the risks associated with murky waters, Superintendent Joseph McNulty urged people to refrain from swimming in the harbour and river systems at this time.