Toxic alert as Hong Kong suffers highest number of red tides in 26 years

The city has been hit by the worst six months of red tides in 26 years, with the highest number of potentially harmful algae species recorded, analysis by the Post has revealed.

Scientific experts said the algal blooms might indicate that pollution is increasing and climate patterns shifting. They would not rule out the possibility that a lethal red tide - that can kill off marine life en masse - could strike soon, although these are almost impossible to forecast.

"The more algal blooms we have, the higher the probability that a toxic red tide will strike," said Professor Rudolf Wu Shiu-sun, director of the University of Hong Kong's school of biological sciences. "Even if they are not toxic, the blooms can still deprive the sea of oxygen and harm fish."

An algal bloom is an area of seawater discoloured by large concentrations of microorganisms, and is often a murky brown rather than red. Peak season is between March and June.

From January up to July, the city had 35 days with red tides - the highest in the six-month period since records peaked at 45 days in 1988. The findings were made in a South China Morning Post review of the Agriculture, Fisheries and Conservation Department's red-tide database.

The natural phenomenon was triggered by 16 algal species, five of which were known to carry potentially harmful effects, the highest number in the same six-month period over the last 26 years. Three of those can release toxins that poison shellfish, while the other two directly harm fish.