Imagining Karachi from a distance brings to mind a picture of the Indus delta where the river deposits millions of tons of silt each year into the Arabian Sea, adding to a complex system of swamps, streams and mangrove forests. Locating the river in Karachi is, however, a challenge. None of its seventeen branches, supposing all of them still exist, looks like a stream of water.

Wandering through Karachi is an encounter with drains full of raw sewage flowing into the Arabian Sea. The dark effluent of the city, disturbingly, makes up for the lack of water in the streams that Indus divides into when it enters its delta. The scale of destruction is enormous.

The Indus has the world's fifth largest delta and the seventh largest mangrove forest system at the tail end of its 3,000 km journey from the Tibetan plateau to the Arabian Sea. World Wild Life Fund puts the area of the delta at about 41,440 square kilometres. The length of the delta where it meets the sea is approximately 210 kilometers.

The annual rainfall it receives is between 25-50 cm in a normal year. Owing to its size, the human population living in the delta area and the diversity of species it supports, the Indus delta was designated a Ramsar Wetland of International Importance in 2002, after the impact on its fragile ecosystem was too evident to ignore. While mangrove forests were threatened, so were a rare species of dolphins in the delta.

The fertile delta land used for agriculture and fishing by villagers has been dying a slow death for years. Rains that feed the Indus delta are insufficient to keep the ecosystem in balance, while fresh river water that nurtures mangrove forests, fisheries, paddy fields and orchards has almost stopped flowing.

Ironically, it was the massive flood of 2010 that brought some relief from salinity to the delta. Fishermen reported higher quantities of fish in near seas. In normal years they fish farther from the shore, as freshwater discharge into the sea is negligible. International Union for Conservation of Nature (IUCN) recommends that 35 million acre feet (MAF) of water should flow down the Kotri barrage to save the river delta.

While the controversial Water Accord, signed by the four provinces, provides that 10 MAF should flow down the Kotri barrage annually and federal agencies claim that this amount flows down the Kotri barrage, there are few takers for the claim. A minister in the Sindh government said at the floor of the house in the last assembly session that water distribution awards were not being observed upstream.

The mighty Indus stinks. Human thirst for water is squeezing life out of the river that has nurtured civilisation for thousands of years in its basin. The Indus combines seven perennial rivers — Indus, Jhelum, Chenab, Sutlej, Ravi, Beas and Kabul — that drain an area of some 950,000 square kilometers. Almost 90 per cent of the water in the upper portion of the river basin comes from glaciers located in the mountain ranges spread across the Tibetan plateau, Jammu and Kashmir, northern Pakistan and Afghanistan.

The Indus river system irrigates 15 million hectares. The irrigation network comprises three major storage reservoirs, 19 barrages, 43 main canals with a conveyance length of 57,000 km, and 89,000 watercourses with a running length of more than 1.65 million km.

The total available freshwater flow in the Indus is about 180 billion cubic meters, 60 per cent of which is used to feed Pakistan's irrigation networks which irrigate about 80 per cent of Pakistan's farmland.  But there is little water left for the delta. As the force of the river has reduced, silt deposited in the delta area by the river has largely diminished flow. Saline water is creeping in, upsetting agriculture and availability of drinking water and causing degradation of ground water aquifers.

As food and water security is threatened, people are displaced. Reports suggest that 1.5 million people have been displaced from Kharochhan, Keti Bandar and Shah Bander areas of the delta to other places. It took the mighty Indus millions of years to create an ecosystem at its delta. It has taken human beings less than a hundred years to threaten its existence.