How rivers are vital for everything from biodiversity to mental health

By Graham Lawton

STAND by a river in the UK and you are in touch with the ancients. Their short, gruff names – Thames, Leith, Taff, Lagan – speak volumes of the history of the islands, from ancient Britons through Romans, Saxons and Vikings. These rivers are part of the past and present. Yet they face an uncertain future.

All over the world, rivers are valuable, often sacred, cultural and practical assets. They are a defining feature of human settlements, exploited for millennia as a source of drinking water, food, irrigation, waste disposal, power, navigation, defence and even inspiration.

In the UK, many of these services are just as relevant today. Tap water comes mostly from rivers. Sewage is disposed into them – preferably treated but often not. Rivers irrigate crops, power homes, take away floodwaters and float boats. Millions of people spend some of their leisure time messing about on, or near, rivers.

The UK is a riverine country. Globally, about 0.8 per cent of the land is covered in freshwater. In the UK, that number is 3 per cent. It has about 1500 river systems, with a combined length of over 200,000 kilometres, ranging from gushing upland headwaters to languid floodplain meanderers, via a vast range of intermediate habitats.

By global standards, these rivers are short, narrow and shallow – “mere streams”, according to the National River Flow Archive at the UK Centre for Ecology & Hydrology in Wallingford. Yet they are extremely diverse in character. According to a recent report by the National Committee UK of the International Union for Conservation of Nature (IUCN), “rivers and their floodplains are among the most important environments in the UK”.

“It’s well known that rivers and their floodplains – and the two go hand in hand – support a disproportionate level of biodiversity relative to their size within landscapes,” says report co-author Stephen Addy at the James Hutton Institute in Aberdeen, UK.

Drinking water and flood management

Although rivers are important for many reasons, their most obvious benefit in the UK is the water they supply. According to Water UK, which represents the country’s water industry, about two-thirds of tap water in England and Wales comes from rivers and the reservoirs and lakes they flow into; the rest is taken from aquifers. Northern Ireland and Scotland rely almost exclusively on rivers, reservoirs and lakes. All told, 87 per cent of the UK water supply comes from these sources.

According to government statistics, water companies in the UK abstract about 4.6 cubic kilometres of river, lake and reservoir water in England for the public supply every year. People drink it, bathe in it, flush their toilets with it, irrigate their gardens with it and use it to wash their clothes, floors and cars. Offices, shops, restaurants and other firms drink deep of it too.

Water is abstracted for other purposes. Electricity generators take 3.4 cubic kilometres to turn their steam turbines, while fish and watercress farms use 0.8 cubic kilometres and agriculture and private water supplies another 0.8. That adds up to a grand total of 9.6 cubic kilometres, equivalent to a cubic tank of water more than 2 kilometres in all dimensions.

Even in a relatively rainy country like the UK, that is milking it. The UK government estimates that about 1 in 5 surface water sources are depleted by over-abstraction, which has knock-on effects on river health.

The opposite problem – too much water – is an increasingly familiar hazard during the winter. Flooding is a growing problem as climate change causes extreme weather events, including biblical downpours. According to the Environment Agency, the UK has had six of its 10 wettest years on record since 1998. Last year was the first to see three named Atlantic storms in the space of a week.

Natural floodplains can help to mitigate flood risk by corralling the excess water and releasing it slowly back into the river. That is especially true of riverine landscapes engineered by beavers, whose dams and pools massively slow the passage of water through the system. Where rain used to hit the ground and surge straight into the waterways, it now is trapped for weeks. Beavers are being reintroduced all over the UK after they gained legal protection last year.

The problem is that many of those floodplains are far from natural, let alone beavered: housing estates and industrial development are often sited on them and these are generally quite useless at mitigating floods.

Water supplies and flood defences are two of many “ecosystem services” supplied by rivers. These are vital goods and services, such as water, pollination and clean air, that flow from nature, or what is increasingly referred to as natural capital.

Economic and health benefits

The UK was the first nation – and remains one of only 26 countries – to audit its natural capital. In 2012, the government established the (now disbanded) Natural Capital Committee (NCC) to advise it on the state of England’s natural capital, in order to help deliver its commitment “to be the first generation to leave the natural environment of England in a better state than it inherited”. In 2020, the NCC published its first set of accounts.

These are by no means complete, as the system for totting up natural capital, called experimental ecosystem accounting, remains a work in progress and nature is complex. But they still speak volumes about the value of rivers.

Water abstraction alone is worth £6.8 billion a year – essentially what it would cost to keep the taps on if rivers didn’t supply the UK with water – and the asset is worth £134 billion (the NCC stressed that these aren’t price tags on nature: given that the natural world supports all life on Earth, its value is infinite). Wetlands sequester 3.5 million tonnes of carbon a year, worth £831 million; that asset is valued at nearly £30 billion. Hydroelectricity generation produces 6865 gigawatt-hours a year, worth £136 million; the value of that asset is £2.2 billion.

These “provisioning and regulating” services are supplemented by some less tangible, but no less valuable cultural services. Around 1 in 10 of the UK’s 5.8 billion annual outdoor recreational and tourist visits are centred on freshwater, worth £681 million; the asset is worth £32 billion. Recreational fishing is a £1.7 billion a year industry. Around 2.7 million people gain health benefits from being in or around freshwater, worth £870 million a year. The asset value of this is nearly £48 billion. Even house prices benefit from the proximity of a river to the tune of £2.9 billion a year.

Essential habitats for biodiversity

One asset that has yet to be incorporated into natural capital accounting is biodiversity, but it is clear that rivers are an important repository of what is left in the UK. Globally, rivers and other bodies of fresh water are disproportionately biodiverse. Despite covering less than 1 per cent of Earth’s surface, they are home to around a third of described species of vertebrate, including approximately 40 per cent of all fish.

The UK’s rivers and the wetlands they feed are disproportionately biodiverse too, though to a lesser extent. They are home to around 10 per cent of the UK’s species, according to the Environment Agency. The IUCN lists 346 river-dependent species, some endangered, including eels, otters, the bar-tailed godwit and feather mosses. The Environment Agency says that over 10 per cent of UK freshwater and wetland species are threatened with extinction.

Rivers are biodiverse in part because they themselves are diverse. A short stretch of lowland river can feature 10 different habitats – pools, riffles (shallow water flowing quickly over stones), glides (deeper, slow-flowing water), backwaters, beds of aquatic vegetation, submerged tree roots, exposed sediment, riverbanks, riparian vegetation and floodplains – all of which provide food and shelter for a different repertoire of species. Further upstream are headwaters, waterfalls and rapids, which also host specialist species such as the freshwater pearl mussel, white-clawed crayfish, brook lamprey and bullhead, as well as juvenile salmon, trout and grey mullet. These juvenile fish will eventually migrate out to sea and become part of the UK fishing industry’s £713 million annual earnings.

Rare chalk streams and poor ecological health

England is also home to the vast majority of the world’s chalk streams, rare and internationally important habitats fed from alkaline aquifers in chalk and characterised by their gravel and flint beds and crystal clear water. They are home to unique ecosystems and have been described as an English Great Barrier Reef. There are only 210 of these waterways in the world and 170 of them are in England (the rest are in northern France).

Unsurprisingly, the value of ecosystem services is strongly related to the ecological state of the asset. In much of the UK, that isn’t a happy tale. England, Wales and Northern Ireland have no rivers considered to be in high ecological health, according to criteria laid down in the four nations’ Water Framework Directives; only 14 per cent are good. The rest are moderate, poor or bad. None is in a good state in terms of chemical pollution and none is in good overall health. In Scotland, 8 per cent of rivers are in high ecological health.

The IUCN report is blunt on this issue, concluding that “truly natural [river] environments that have escaped both direct and indirect human alteration no longer exist”. However, there is hope, according to Addy. “There are some grounds for being optimistic. River restoration in the UK is undergoing a step change, there are more and more projects going on everywhere.”