Five red tides have been sighted in Hong Kong waters in the past week.

Leisure & Cultural Services Department staff saw a red tide at Clear Water Bay's First and Second Beaches on August 27. Red flags were hoisted until August 31 when both red tides dissipated.

Red tides were also seen in the Shing Mun River on August 27, Tai Tau Chau and Kai Lung Wan on August 31, and from Yung Shue Au to Kat O on September 1. The one at Shing Mun River dissipated on August 30 while the other two still persist.

The Shing Mun River tide was formed by Haematococcus pluvialis which is rare in Hong Kong waters, while the rest were formed by Prorocentrum micans which is common. Both are non-toxic.

The Agriculture, Fisheries & Conservation Department has stepped up red tide monitoring and informed mariculturists in concerned fish culture zones, including Tai Tau Chau, Kai Lung Wan, Shau Tau Kok and Kat O.

Red tide is a natural phenomenon. The department's phytoplankton monitoring programme will continue monitoring red tide occurrences to minimise the impact on the mariculture industry and the public.