The Indus River, which flows through the heart of Pakistan for most of its length, is the 22nd longest river in the world and the 9th longest in Asia. Statistically, it may not sound all that impressive, but this big river has played a crucial role in the history and ecology of the region and continues to be a significant factor today.

The Indus River

The Indus River begins its long, over 2,000-mile journey in the mountains of southwestern Tibet Autonomous Region of China, near Lake Mapam, at a staggering elevation of nearly 18,000 feet. The river runs briefly through Tibet, technically part of China, through a few states of India and the disputed territory of Kashmir, before making its way into the mountains of northern Pakistan.

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The source of the mighty Indus is a modest mountain spring, but as the river gathers speed coming down the mountains of the Himalayan, Karakoram, and the Hindu Kush ranges, it is fed by both tributaries and melting mountain glaciers. The main tributaries of the Indus are the Zanskar, Chenab, Shyok, Gilgit, Kabul, Gomal, and Kurram Rivers. With all these inputs to the river, the Indus has a total annual flow of around 50 cubic miles, which places it among the mightiest and largest of all the world’s rivers.

After the Indus leaves the mountain ranges, it emerges onto the Punjab plain where it moves much more slowly and deposits silt collected from the mountains. During the flooding season, which lasts from July to September, the Indus can grow to several miles wide in places. The Indus reaches its conclusion at the Indus River Delta where the river enters the Arabian Sea of the Indian Ocean. The delta covers about 3,000 square miles and provides a unique environment for plants, animals, and humans.

The Indus Ecosystem and Overuse

The Indus River Valley is one of the driest regions in southern Asia. Much of the river’s volume is provided through snowmelt from the mountains and glaciers, tributaries, and monsoon season. Because of the arid environment, there is little vegetation along much of the Indus. However, in the river itself are a number of fish species, 22 of which are found nowhere else in the world. One of the rarest mammals in the world also lives in the river and nowhere else: the Indus River dolphin. This blind river dolphin is highly endangered, and there may be only 1,000 or fewer left living.

The delta of the river represents a separate and unique ecosystem. Here the river spreads out into hundreds of streams and marshes. It is home to the world’s largest mangrove forest and serves as a temporary home for millions of migrating birds. Fish and other animals unique to the Indus Delta include the Rita catfish, the Hilsa shad, and the giant snakehead, a fish that can grow to six feet long.

The Indus River Delta is a special ecosystem and it is also a threatened one. The Indus Valley is the breadbasket of Pakistan, but because of its aridity, water needs to be taken from the river to irrigate crops. The river has been so overused by the growing population of the country that the delta is shrinking and salt water from the ocean is intruding further inland, destroying valuable and beautiful ecosystems. The fertile fisheries and rice paddies of the delta are shriveling up and disappearing rapidly.

Human History Along the Indus River

Modern people are not the only ones to have depended on the waters of the Indus River. People have made use of it for millennia. One of the biggest and oldest civilizations in the world, called the Indus Valley Civilization, lived along the river between 7500 and 1300 B.C. Archaeological excavations have uncovered major ancient cities here and have found that the demise of the civilization was likely because of climate change. The region around the river became cooler and drier around 1800 B.C. and the river could no longer provide enough food and water.

Lesson Summary

The Indus River begins in Tibet and flows through Pakistan to the Indian Ocean. The river is fed by glaciers, snow melt, and tributaries, and it floods during monsoon season from July to September. The Indus emerges in a 3,000-square mile delta, however this area is shrinking. The river is used to irrigate crops in the valley, and this use is rapidly decreasing the delta. The river and delta are home to unique species, including the endangered Indus River dolphin. For thousands of years, the Indus Valley Civilization, an ancient civilization known for its cities, technology, and art, flourished along the river only to decline due to climate change.