Explainer | How red tides occur, why they smell bad, why you should not swim in one and why your dog should stay out of the water
- Red tides are blooms formed by millions of algae when sea conditions are right, usually in spring. They often turn a reddish colour, and at night glow blue
- Usually they are harmless, but some can make people very ill if they come into contact. Dogs that enter a red tide or eat poisoned fish can be affected too
Red tides returned to Hong Kong shores this week.
A natural phenomenon caused by large concentrations of microscopic algal blooms, the latest ones involved Noctiluca scintillans, a non-toxic species of plankton common in Hong Kong waters, says the city government’s interdepartmental red tide working group.
Red tides were spotted on the south side of Hong Kong Island, in Victoria Harbour and on outlying Lamma Island. “Given the wide extent of these current red tides, the situation may last for several days,” said a group spokesman.
Internet users took to social media to share sightings of the rust-coloured patches which, at night, through a chemical reaction called bioluminescence, create a blue fluorescent glow known as “blue tears”.
Last weekend, the coasts of Sai Kung in the New Territories were flooded with blue tears, a beautiful spectacle but one that can harm marine life.
