A 39-year-old surfer was bitten by a shark near the Point Plomer campground on Tuesday morning. He was taken to hospital with minor injuries and is in stable condition. This incident is the fourth shark attack in New South Wales within 48 hours. Recent attacks have left two people critically injured and others with wounds, including a 12-year-old boy and an 11-year-old surfer. Steven Pearce, Surf Life Saving NSW chief executive, warned, "If anyone’s thinking of heading into the surf this morning, anywhere along the northern beaches, think again. We have such poor water quality that’s conducive to bull shark activity. We have two people critically injured in hospital this morning. Just go to a local pool, because at this stage, we’re advising that the beaches are unsafe." Surf Life Saving NSW launched drone surveillance and sent lifeguards on jetskis near Crescent Head. The beaches between Town beach and Crescent Head have been closed following the shark bite. NSW Department of Primary Industries is monitoring the situation and will release a statement later. Experts say heavy rains have made Sydney's waters murky and brackish, attracting bull sharks closer to beaches and estuaries. Bull sharks can tolerate freshwater, increasing their movement near river mouths after rain. Jodie Rummer, marine biology professor at James Cook University, said, "Bull sharks are also one of the few species of sharks and rays that can tolerate brackish and even freshwater for extended periods, which means they are especially comfortable moving in and out of river mouths and turbid coastal waters after heavy rain. We also have more people in the water than ever before, which naturally increases the chance of encounters. The key message is being shark smart." NSW police urge the public to stay out of the water especially after heavy rain. All beaches on Sydney’s northern shores remain closed until at least Thursday. General safety advice urges swimming in groups, avoiding dawn and dusk swims, and steering clear of murky waters, especially near estuaries.