What’s Causing the Unpleasant Smell in Karachi? A Look at the Recent Coastal Phenomenon

Karachi’s coastal areas have plagued by a strong, unpleasant odor recently, sparking concerns among residents and visitors alike. The smell, particularly noticeable after the recent monsoon rains and tidal surges, is not an uncommon phenomenon in the city. But what exactly is behind this foul odor?

The Source: Phytoplankton Decay

Experts have traced the smell to the decay of marine plants, specifically phytoplankton, which accumulate along Karachi’s shores after the monsoon season. Mohammad Moazzam Khan, an adviser at the World Wide Fund (WWF) Pakistan, explains that the stench is the result of rotting phytoplankton, which wash ashore and decompose as the monsoon winds down.

“These microscopic plants can cause the sea’s color to shift to green and may even be toxic, leading to increased marine life mortality,” Khan said. He further pointed out that one particular species, Noctiluca scintillans—commonly known as Sea Sparkle—is part of the phytoplankton group responsible for this unpleasant smell.

Why Does Phytoplankton Cause the Smell?

Phytoplankton, while essential for marine ecosystems, can become problematic when they proliferate in large numbers. During the monsoon season, these organisms thrive in the coastal waters, often forming massive blooms. As the monsoon subsides, the phytoplankton die off and wash ashore, where they begin to decompose. This decomposition process emits a strong odor, which can linger for several hours or even days, depending on the size of the bloom and weather conditions.

Noctiluca scintillans, in particular, has known for its toxic blooms. These blooms, while visually captivating (sometimes causing the sea to glow at night), can result in mass deaths of marine animals and are notorious for their unpleasant smell during decomposition.

Seasonal Patterns and Environmental Impact

This issue tends to arise during specific times of the year, especially in the pre-monsoon (April to May) and post-monsoon (September) periods when phytoplankton blooms are most prominent. The warmer waters and nutrient-rich conditions created by the monsoon rains provide the perfect environment for these organisms to flourish.

While the smell is a nuisance, phytoplankton play a vital role in the Earth’s ecosystem. They are responsible for producing nearly two-thirds of the planet’s oxygen and are fundamental to marine food chains. Their presence, in normal quantities, supports marine life and helps maintain ecological balance.

A Broader Environmental Concern

The stench emanating from Karachi’s coastline is a reminder of the delicate balance in marine ecosystems. While phytoplankton blooms are natural, experts have raised concerns about increasing pollution and warming sea temperatures, which can exacerbate these blooms. Excess nutrients from sewage and industrial runoff can fuel larger and more frequent phytoplankton blooms, leading to increased mortality among marine species and contributing to the foul odors that follow their decay.

The recent unpleasant smell along Karachi’s coast has a seasonal issue caused by the decomposition of phytoplankton that bloom during and after the monsoon season. While these organisms are crucial for the environment, their excessive growth and subsequent decay create an unavoidable odor. However, the situation also highlights the need for better environmental management of coastal areas to mitigate pollution, which can intensify such natural phenomena. As Karachi continues to grow, addressing the factors that contribute to these occurrences will be key to maintaining a healthier coastal ecosystem.