SEVEN beaches were closed to the public yesterday due to Red Tide, the algae's first major return since it wiped out large stocks of fish earlier this year. Fishermen have been warned about the spread, which was first spotted around Lamma two days ago. While the present variety is non-toxic, there is a danger that because the spread is so large - covering the water at Shek O, Big Wave Bay, Repulse Bay Beach, Middle Bay Beach, Chung Hom Kok Beach, Stanley Main Beach and Hairpin Beach - it could reduce the amount of oxygen in the water. 'The mariculturists have been notified and they know to pump oxygen into the water if necessary,' said a spokesman for the Agriculture and Fisheries Department. The Marine Police spotted the algae yesterday around Deep Water Bay and Middle Island. They took samples for the Agriculture and Fisheries Department, which concluded that it was the single cell ocean organism 'mesodinium rubrum'. The Urban Services Department has hoisted the red flag until further notice. The Government still does not have a tracking system to follow the spread of the organism despite the loss of fish stocks in April when beaches were choked with a lethal variety.