A fluorescent blue glow seen emanating this week from the coastal waters along Lung Mei, Tai Po - the future site of a controversial man-made beach - may look beautiful, but environmental advocates say it signals trouble. The otherworldly colour comes from an algae bloom called Noctiluca scintillans , nicknamed "sea sparkle", which is a kind of red tide whose growth is stimulated by organic pollutants such as sewage, green groups say. The luminescent patches, seen near Sam Mun Tsai and Lung Mei villages in the past two weeks, are formed by the glow of a single-cell organism which has a heart shape and a tail, said Dickson Wong Chi-chun of the Hong Kong Wildlife Forum. "It is transparent and appears pink in day time," he said. The blue glow is triggered when the organism is disturbed by waves, ships or humans. Most bioluminescence appears as a blue or green colour as those use less energy than red, he added. The sparkles are usually spotted in Tolo Harbour starting in March, but warmer than usual seawater temperatures could have triggered an early emergence, Wong said. DON'T MISS: Hong Kong in bloom - stunning photos of 'Sea Sparkle' on city’s shores Dr Michelle Cheung Ma-shan, science manager at the Eco-Education and Resources Centre, said the kind of red tide that causes the glow is usually non-toxic. Still, she advised against getting into the water to see the algae. "They are there because of the presence of organic pollutants, which could include waste water from the toilet. You won't want to meddle with them," she said. People with allergies and children should stay away, she cautioned. She also noted that the organism could use up oxygen in the water and kill fish, if enough of it was present. In 2012, the group found sea snails with defective sex organs, signalling the presence of a toxic chemical, in Lung Mei. In August, the courts dismissed a judicial challenge filed by green activists who wanted to stop plans to build a beach at Lung Mei. To ensure the beach is hygienic enough for swimming, the government vowed to fix the sewage discharge from village houses if the plan went ahead. In the meantime, however, there are no signs of beach construction, nor of repairs to the sewage system. According to the Environmental Protection Department, water quality has improved in Tolo Harbour in the past decades, with the number of red tides dropping from 43 in 1988 to less than 20 in recent years. Red tides are common in Tolo Harbour due to its enclosed nature and low water exchange rate, Cheung said.