An inter-departmental red tide working group reported that Environmental Protection Department staff saw the red tide patch about 10 kilometres off the island on October 13.

It was formed by Trichodesmium thiebautii - which has not been seen in Hong Kong before - and Trichodesmium erythraeum, which is rare in local waters.

Although overseas studies show that both species might contain toxins, no toxic effect caused by these two species has been recorded in Hong Kong waters before.

The Agriculture, Fisheries & Conservation Department notified fish farmers in the Tung Lung, Po Toi O, Kau Sai and Leung Shuen Wan fish culture zones of the red tide and urged them to monitor the situation closely. No associated fish deaths were reported.

Red tide is a natural phenomenon. The AFCD's phytoplankton monitoring programme tracks red tide occurrences to minimise the impact on the mariculture industry.