A member of the public observed a red tide at Rambler Channel near Hoi Hing Road while staff of the Agriculture, Fisheries and Conservation Department (AFCD) sighted red tides at the western waters of Lantau Island and Tsing Yi on 18 March.
The red tides still persist. No associated death of fish has been reported by mariculturists so far.
"Both red tides were formed by Noctiluca scintillans, which is common in Hong Kong waters and non-toxic," a spokesman for the working group said.
The AFCD urged mariculturists at Ma Wan and Cheung Sha Wan Fish Culture Zones to monitor the situation closely.
Red tide is a natural phenomenon. The AFCD's proactive phytoplankton monitoring programme will continue monitoring red tide occurrences to minimise the impact on the mariculture industry and the public.