The demands posed by burgeoning population growth are placing unprecedented stresses on the world’s great rivers. All large rivers are hotspots of resources, agriculture, trade, and energy production and flow through developing nations, where much of the population is vulnerable to environmental and ecological stresses. If appropriate policies are not framed with urgent interventions, humanity will see the planet’s diverse ecosystem collapse in the coming decades.

Despite humaninduced adverse changes with many large rivers, the current coronavirus pandemic is already influencing regulatory frameworks as observed in India, United States and also in other countries. In India, the changes made in the draft EIA 2020 are completely contrary to the principles of environment protection and sustainable development with reference to EIA notification 2006.

The US government has eased its enforcement of pollution monitoring, enabling polluters to avoid penalties. These anthropogenic stressors function on a range of timescales, and their effects potentially amplify the risks posed by extreme climate events and thereby increase the likelihood that key resilience thresholds will be crossed.

Most importantly, the strong link between ecosystem services and livelihoods acts as a severe stressor that causes major barriers towards meeting the UN Sustainable Development Goals by 2030. Among the many major rivers in the world, the Ganges covering a distance of 2,600 km eventually becomes one of the planet’s most polluted rivers, a mélange of urban sewage, animal waste, pesticides, fertilizers, industrial metals, rivulets of ashes from cremated bodies and many more.

The bacterial levels are remarkably high. Despite so much pollution, its numerous watersheds in the mountains, across the Deccan Plateau and its vast delta serve 400 million people — a third of India’s population — as a source of drinking water for humans and animals, essential for crop irrigation, travel and fishing. Rivers have assimilative capacity for responding to upset of equilibrium in water quality or sediment load through self-adjusting processes of erosion and sedimentation.

These responses typically involve feedbacks that impart some resilience, allowing rivers to absorb a degree of change. Climate change, as manifested through a complex global pattern of future floods and droughts, presents a background stress that is increasing through time and pushing this flexibility to its limits. River resilience can further be lowered by a range of other anthropogenic stressors that could present slow ongoing changes or extreme events that operate over short timescales.

For example, the severity of flood in Kerala that killed at least 370 people, displaced 780,000 and caused Rs 30,000-50,000 crore worth of damage may be attributed to the ways in which river channels are engineered. The disaster with signi?cant consequences may be attributed to poor water governance in India. Thereby reduction in resilience makes river systems more vulnerable to the increasing magnitude and frequency of such extremes, which increases the likelihood that the tipping point for system resilience will be crossed.

Such changes can have immediate consequences, such as hazardous riverbank erosion, which damages infrastructure and threatens lives, but could also impose a legacy of change that persists for centuries. Changing river flows also modulate the movement of sediment to floodplains and deltas. Timescales of effects for climate-related changes in river flows, and their extremes, range from decades to hundreds of years.

In addition, landuse changes, such as deforestation or reforestation of catchment hill slopes and floodplains, can modify the quantity of water and sediment entering rivers through soil and bank erosion over similarly wideranging timescales. The construction of many large dams all the over world for hydropower, flood control, irrigation, and water supply is booming. Many of them are already constructed and many more dams are either under construction or are being planned.

If all the dams are constructed, the number of freeflowing rivers would not only be drastically reduced but also these dams will trap sediment, alter flow regimes, trigger riverbed incision and bank instability, and in tropical regions, cause substantial emission of the potent greenhouse gas (GHG) methane as a result of vegetation decay. Such effects are compounded by water diversions and the interlinking of rivers within, and between, river basins. In this way the riverine ecology has been completely jeopardized.

In addition to this destruction in the name of development, sand and gravel mining are destroying riverbeds across the globe. Further, the introduction of non-native species – such as fish, invertebrates, and vegetation – can have almost immediate ecological effects and economic consequences, potentially compounded by river interlinking. Pollution from industrial, domestic, and agricultural sources could pose a near instant threat.

The water quality deteriorates severely on account of pollution from nitrogen, phosphorus and sediment, three ingredients that in high quantities can cause numerous environmental problems in streams, rivers and bays. Water pollution is a problem that affects both rich and poor countries, however the cocktail of chemicals changes as countries develop. In poor countries it is faecal bacteria and as GDP increases then nitrogen and phosphorous due to use of chemical fertilizer becomes the issue.

Recently researchers have revealed riverine antibiotic pollution originating from human and animal waste and leaks from wastewater treatment plants and chemical factories. Such potent antibiotic pollution is present worldwide and aids the development of antimicrobial resistance. Another major stressor is sediment starvation due to declining river sediment loads caused by the changing frequency of extreme events; sediment trapping behind dams, large-scale mining of river sand.

The combined impacts are so large that riverbed levels have lowered by about 2–3 m in only the last decade, destabilizing river banks and enabling saltwater incursion at high tide, posing a severe threat to agricultural production. Anthropogenic pressures are now so great and so rapid that there is a clear danger of imminent, and irreparable, environmental change.

The environmental improvement that the world observed during lockdown is clear evidence that if effective interventions are made, cleanliness of river is possible. A range of measures along some rivers, including dredging of plastic, relocating factories and controlling waste discharge from industries and domestic sources and banning single-use plastic goods, are having major effects in reducing pollution.

At the same time, it is also true that governments and bureaucracies sometimes ignore environmental problems. Despite so many constraints, international institutions must provide a channel for scientific advice and help support local, national and transnational river-management organizations. Further, river governance must include local stakeholders and incorporate issues of social equity, inclusivity, and gender.

Creative financial instruments are also essential to deliver the investment necessary to fund restoration, protection, and management. If we fail to do all this, in 50 years our despairing descendants will be baffled by our inaction. If governments fail to take effective measures, the environmental movement needs be energised to stop environmental damage.

(The writer is former Senior Scientist, Central Pollution Control Board)