Every day, more than 300 million gallons of waste is generated in Karachi, out of which 40% is domestic waste and 60% is industrial waste. The sea receives over 150 million gallons of untreated domestic, municipal and industrial effluents daily which is dumped via Malir River, Lyari River and small waste drains mainly along Clifton coast and Korangi coast.

According to a report of Karachi Water and Sewerage Board (KWSB), the official sewerage system in Karachi serves only 40% of the cityís population. Of the 350mgd (million gallons daily) of the waste water is produced every day, only 40mgd is treated by the official systems. The rest goes untreated into the open sea through drains.

The KWSB, instead of developing an efficient sewerage system connected to the sewerage pipeline, easily allows untreated sewage to flow into the sea, thus damaging the sea environment. The Arabian Sea has been immensely polluted due the 4 trillion gallons of untreated sewerage that have already been carelessly poured into it.

While most animals and plants are less affected by pollutants, there are other particular species which undergo drastic changes in their behaviour. The pollutants cause eutrophication i.e. manuring of the sea through effluents which come from households and industries. Since the free-swimming micro algae rely on these effluents for nutrition, these organisms start reproducing themselves in great quantities. When they die, they sink to the sea-bed and their decomposition causes a very high loss of oxygen in water which creates sludge, and directly causes a hindrance in the fichesí ability to metabolize and swim.

The concentration of sediments is normally around 50,000-200,000 parts per million (ppm) with sometimes going up to 600,000 ppm, which causes destruction of aquatic organisms.

Enforced eutrophication leads to changes in the balance of marine ecosystems, which can be advantageous for the growth of certain unwanted algae but not for others which are of high value to the food chain. Moreover, dolphins, tortoises, whales and other mammals die as a result of excess liquid sewage and oil pollution because their nostrils get blocked and their eyes get inflamed.

Industrial sewage contains chemical pollutants that enter the sea and contaminate the water. This pollution is then transferred into the aquatic vegetation which is consumed by smaller marine organisms like fish, crab, lobsters, shrimps etc.

Marine life forms do not die out due to consumptions of these heavy metals. In fact, these toxic metals stored in their fats are consumed by the bigger marine animals which mean transferring the pollution load to their predators. The level of contamination increases, and when these contaminated marine species are consumed by humans, it creates serious health problems, sometimes proving fatal.

These heavy and toxic metals have carcinogenic qualities and can cause genetic deformation, besides affecting other vital organs like brain, heart, kidney, lungs and bones of the human body.

Wastewater flows are about 1,000 million liters per day at present, and this figure is projected to increase to over 3,000 ml/day by 2025, resulting in low level of dissolved oxygen for marine life. Based on an average Biological Oxygen Demand (BOD) strength of 400 tonnes per day, the total BOD load is expected to rise at about a level of 1200 t/d by 2025, as most of this waste water is discharged into the rivers without treatment. Fish becomes scarce if there is a reduction in oxygen amount and results in anaerobic bacteria.

Although it has been found that heavy marine pollution due to sewage may not be harmful for the mangroves, but then again, it can prove to be unsafe for certain species of fish who feed on them. The leaves litter of mangroves is a major source of nutrient and provides a diverse habitat for almost 90% of tropical marine species, invertebrates, birds and reptiles.

To top it, the leather tannery discharge from industries combined with over fishing and mangrove destruction is also contributing to a sharp decline in shrimp finfish production.

Marine fish landings in Pakistan are approximately a total of 0.4 million MT per year, out of which 30,000 MT are of Peneid shrimps that not only constitute to the backbone of the local marine fishing industry but are also an important source of foreign exchange for Pakistan as a whole. But this loss of shrimp due t the heavy pollution is having a devastating effect on the fishing industry.

The Pakistani government tested the effluents run-off from leather tanneries and verified that the discharge were toxic and is uncontrolled by any process treatment, waste cycling or end of pipe treatment.

The domestic sewage usually consists of an abundance of used plastic bags that not only choke the drainage pipes, but are extremely harmful for marine life as well. The polythene bags that are discharged into the sea along with the liquid waste become heavy with oil, which is also a pollutant, and settle down on the sea-bed. This in turn prevents the hatching of fishesí eggs which usually get trapped in the oil present in the polythene bags. If only these bags are taken out from the sea, our fishing production would double and our earnings through fish exports could increase from Rs. 7-8 billion presently, to Rs. 12-13 billion!

However, a report from the National Institute of Oceanography reveals that most of our coastal area is virtually free from pollution because the coastal belt of Pakistan is thinly populated and is almost devoid of industries except for Karachi, where the greatest amount of pollution occurs.

It also stated that a geographical information system i.e. a plan to map all areas under the sea, after every ten meters, is also being considered so that an accurate detection of the fishís trail and its breeding ground is possible.

Sources said that a grant of about Rs.12 million was received from the Asian Development Bank (ADB) with the help of which the government has planned to fix 50 treatment plants for sewage filtration within the next five years. Another endowment was received from Japan International Cooperation Agency (Jica) of Rs.789.623 million in the form of machineries. Many other countries, including USA are also participating for revamping the sewerage and drainage system to meet their own demands for clean fish.

In the last few years, several incidents of mass mortality of fishes have been recorded in the marine coastal environment of Pakistan. It is also observed that unusual mortality fish in the Arabian Sea has increased in the last few years which has had an adverse effect on fish marketing and fisheries industries.

It is true that we cannot completely prevent the pollution of the sea. But a calculation of the consequences can be learnt and possible preventive measures can be taken to task.