The red tide gets its name from the tinge that colours the sea when it is filled with algae carrying toxic substances. When these are released into the water the fish suffocate. Humans entering the affected water suffer from skin irritations, vomiting, diarrhoea and, in extreme cases, paralysis.
Mr Sham graphically described the speed with which the red tide moves: "Within a couple of hours it multiplies to a level that the fish cannot tolerate and they are wiped out." The waters around Hong Kong are filled with the inert bodies of dead fish floating on the surface surrounded by a blood-coloured murky mess.
The authorities are not sure why this year's red tide is so much worse than previously, when it came and went much more quickly. One theory is that Hong Kong has fallen victim to climatic changes induced by the phenomenon El Nino, which have been warming the oceans and causing droughts elsewhere in Asia.
The environmental group Friends of the Earth in Hong Kong is convinced that the problem has been worsened by the illegal discharge of industrial waste into the sea by heavy industries in southern China.
Meanwhile, Hong Kong island beaches, which are usually filled to capacity over the holiday weekend, were dominated by red flags warning people not to enter the water. The warning was widely heeded, although some swimmers seemed oblivious to the risk.
Although the algae which kills fish and affects humans is clearly toxic, the government has told Hong Kong residents that it is safe to eat the dead fish. Government experts maintain the algae affects the fishes' respiratory system but will not harm humans eating the carcasses. This view is challenged by those who believe that the poison enters into other parts of the body.
"I won't say it's under control but I would say the situation has stabilised," said Mr Sham, who now faces the problem of dealing with a mountain of compensation claims from fish farmers.
Nature has not been kind to Hong Kong since China resumed sovereignty over the territory last July. First, it was hit by unprecedented torrential rains, then there was the outbreak of bird flu, which led to the slaughter of all the territory's chickens. Now fish, the other staple item of the Cantonese diet, is under threat, too.