Karachi's foul smell traced to rotting phytoplankton, WWF says; sea breeze to clear it

Karachi woke up to a strong rotten smell on Wednesday, 16 September, and by mid-morning complaints were coming from Clifton, DHA, PECHS, SMCHS, Korangi, Saddar and as far inland as Orangi, North Nazimabad and Federal B Area. The cause, according to WWF-Pakistan, is natural: dead and decaying phytoplankton in the sea off the city.

What caused the smell

Phytoplankton are microscopic marine plants. During the monsoon they multiply fast in the warm, nutrient-rich water along the Sindh coast. When the season turns, usually around mid-September, changes in water temperature, currents and wind kill them off in large numbers, and the rotting mass gives off the stench.

Muhammad Moazzam Khan, technical adviser on marine resources at WWF-Pakistan, told reporters the odour along the coastal belt came from the rotting of these marine plants and called it a naturally occurring event. He said a similar smell had been noticed along the Gwadar coast about three days earlier.

Why it spread across the city

Weather made it worse. The Pakistan Meteorological Department (PMD) said sea breezes were weak from Tuesday night into Wednesday morning, so the smell sat over the city instead of blowing away. A PMD spokesperson also pointed to a low-pressure area over the Arabian Sea and southeasterly winds.

By Wednesday evening winds had picked up to about 22 km per hour, and the PMD expected the normal southwesterly sea breeze to be fully active by Thursday, which should clear the air. The Met Office forecast hot and humid weather for the city.

This has happened before. In June 2017, WWF-Pakistan linked a similar citywide stench to a decaying bloom of Noctiluca scintillans, the plankton known as sea sparkle.

Is it dangerous?

Experts quoted by Dawn and The Express Tribune said there is little reason for alarm and that the smell should fade within days. We could not find any public health advisory from the Sindh government, the Sindh Environmental Protection Agency or the Karachi Metropolitan Corporation as of Thursday morning.

An ecologist quoted by Dawn in an earlier episode said long exposure to the smell combined with dusty winds might bother people with sinus problems, though there was no firm evidence.

What you can do

• If the smell is strong in your area, keep windows shut during the worst hours and air the house once the evening sea breeze picks up.
• People with asthma, sinusitis or other breathing problems may want to avoid long walks on Clifton Beach, Sea View or Do Darya until it clears.
• Keep children and pets away from any dead marine matter washed up on the sand.
• If you have breathing trouble, see a doctor rather than waiting it out.

Hot, humid days also push up cooling costs. You can estimate yours with our AC running cost calculator or check your bill with the electricity bill calculator.