Across the world, lakes fed by rivers, glacial melt, groundwater, rain and snow have played an important role in human civilization, culture and development. They contain most of the liquid fresh water on the planet’s surface, house an array of wildlife, and make farming, fishing and industry possible. They also play an important role in water storage, aquifer recharge and air temperature regulation. Yet, due to climate change, pollution, mining, population pressure, and unsustainable use, they are declining at an unprecedented rate. Freshwater ecosystems have lost more extent and biodiversity than almost any ecosystem in the world.
The planet’s more than 3 million lakes vary enormously in terms of their salinity and chemical composition, area, depth, biodiversity, the volume of water they store, their ownership (whether publicly or privately owned), the extent to which they are polluted, the rate at which they are shrinking, and more. Lake Baikal in Russia is estimated to contain 20 % of the planet’s liquid freshwater resources – about the same as all the North American Great Lakes combined. The largest lake in terms of area is the Caspian Sea, which has varying levels of salinity. Lake Natron in Tanzania is one of the most alkaline lakes in the world. Utah’s shrinking Great Salt Lake is releasing toxic dust from exposed lake beds. Lake Van in eastern Turkey is an example of an endorheic lake – it has no natural outlet.
The threats facing lakes are interlinked. Lake pollution is frequently caused by inflows from nutrients , surface-bound contaminants and solid waste being dumped directly or flushed into lakes via rivers, and this is worsened by global heating – leading, for instance, to more frequent and intense floods. UNEP’s 2021 flagship report Making Peace With Nature notes that “water pollution has continued to worsen over the last two decades, increasing the threats to freshwater ecosystems and human health.”
Fertilizer is an important component of modern food systems, and yet it is also a major source of river and lake pollution through nitrogen and phosphorus accumulation. Rain washes the nutrients in fertilizer into waterways and lakes which can lead to damaging algal blooms, which are predicted to increase by at least 20% by 2050 and are already a serious challenge and intensifying in global freshwater lakes.
Wastewater is another pollution threat. Billions of people are still lacking safely managed sanitation, and up to 80 % of global wastewater is estimated to enter water bodies untreated with adverse impacts on human and ecosystem health.
The water levels of lakes are also changing dramatically. Rising temperatures and changes to cloud cover, which are leading to decreasing ice cover, are increasing the rate of water evaporation. A new global study covering a staggering 1.42 million lakes suggests evaporation is causing them to shrink faster than previously thought. Climate change is also causing glacier melt which can lead to the threat of glacial lake outbursts that can devastate downstream communities.