Sea beaches around HongKong have a problem. They regularly face the threat of a ‘Red Tide’.

The ‘Red Tide’ kills fish in sea farms and in the open seas. Actually, the ‘Red Tide’ is reddish brown algae that floats on water near the coastline. It enters the gills of the fish swimming about in the sea and kills them.

The gills are like noses of the fish. They help the fish breathe. When the algae enters the gills, it creates havoc.

The algae-infected gills fills with mucus and the fish die because they cannot breathe. Their noses do not get any oxygen.

Algae can live in water and in moist soils. Like any other plant, they also use the green pigment chlorophyll to make food. But sometimes, the green pigment is covered by another coloured pigment. So algae may have various colours, like blue-green, red, yellow-green and brown. They make their own food and are a source of food for fish.

Dangerous Red Tide in HongKong
Dangerous Red Tide in HongKong [Illustration by Sudheer Nath]

But when fish approach them for food, some of them enter the fish’s gills, leading to disaster.

Nearly 1,500 tons of fish have died in sea water fish farms in the recent past. As a result bodies of dead fish often float near the coast of HongKong.

Initially, the Hong Kong authorities were not concerned about the algae menace. They thought it was because of sewage pollution.

Sometimes, chemicals thrown into the sea brings about the growth of algae. If this happens in lakes and ponds, fish die as algae remove all the oxygen from the water by their rapid growth.

Now the evergrowing reddish brown algae has left the authorities worried. Because it is not connected to sewage. And it could prove to be a health hazard too. As algae-infected fish are poisonous and could lead to loss of human lives.