The Covid-19 pandemic has led to a surge in wild swimming in the UK. With pools closed and citizens encouraged to exercise near their homes, many took up swimming in rivers, lakes and lochs, as well as the sea, encouraged by claims of physical and mental health benefits. As a result, there is now considerably more public scrutiny of the quality of natural bodies of water, particularly rivers.

The quality of water in rivers is predominantly governed by the Water Framework Directive (WFD), an EU directive adopted throughout Europe in 2000 and implemented through domestic legislation in the individual regions of the UK. The directive set out standards for the quality of surface water bodies and said that waters must achieve ‘good’ ecological and chemical status by 2015, which has since been extended to 2027. 

Ecological status is based on levels of aquatic flora and fish fauna, the availability of nutrients, and aspects including salinity, temperature and chemical pollutants. Morphological features such as quantity, water flow, water depths and structures of the riverbeds are also taken into account. Chemical status is based on levels of more than 40 chemical pollutants.

The Water Quality in Rivers report, published by the UK government’s Environmental Audit Committee in January 2022 following its inquiry into the water quality of rivers, says that only 14% of rivers in England achieve the ‘good’ ecological standard and none meet the ‘good’ chemical standard. The situation is better elsewhere in the UK, but no region is yet meeting the requirements of the WFD.

The inquiry found that the main reasons for not achieving the required standard were:

1. Agricultural pollution from rural areas (affecting 40% of water bodies)
2. Sewage and wastewater (36%)
3. Urban diffuse pollution (run-off from towns, cities and transport – 18%)

The WFD focuses on the ecological quality and chemical composition of river water; it does not require water to meet standards suitable for bathing or swimming. However, the pollutants associated with agricultural run-off, sewage and urban run-off can pose potential risks to people using rivers for recreation. In her evidence to the government committee, Swim England chief executive Jane Nickerson said: “Most people who go swimming in open water do not realise the risks they are taking.”

The quality of bathing water is governed by another EU directive – the Bathing Water Directive (BWD) which, again, is enshrined in the domestic laws of all four nations (see the table below). This directive first came into force in 1976 but was fully implemented in the UK only in 2015.

The BWD includes a classification system for water quality and puts an emphasis on informing the public about bathing water quality and potential threats to public health. However, these quality standards apply only to locations that have been given designated Bathing Water Status.

The UK has more than 600 designated bathing waters, but almost all are coastal sites – the list includes only 16 lakes and lochs and one river, a section of the River Wharfe in Ilkley, West Yorkshire. More are likely to follow: a second application is being considered for two sites on the River Thames in Oxford, and Severn Trent Water has set out ambitious plans to deliver bathing quality water in two rivers in its region – the Avon and Teme. 

Still, most other European countries have far more designated freshwater bathing sites, as shown on the map below. For Ian Dunhill, senior advisor, bathing water at the Environment Agency, the low number of rivers designated as bathing waters in the UK is indicative of cultural norms. He said: “It’s traditions. The British tradition has been to go to the seaside, that’s where our emphasis has been.”

Bathing Water Status does not give any indication of water quality. Designation is granted on the basis that the location is popular for swimming and bathing, not because the water is suitable for swimming in. However, once a site is designated as such, the water quality has be monitored regularly – at least four times a year during the bathing season – and the local council must display information about water quality and pollution sources. The monitoring organisation identifies the site where the testing takes place based on where people are most likely to swim and where pollution inputs will be picked up. Details of monitoring organisations and bathing water seasons in the UK are listed in the table below.

The Bathing Water Directive defines a bathing water as a location where a large number of people are expected to bathe and where a permanent bathing prohibition, or permanent advice against bathing, has not been issued.

Generally, large numbers of bathers are found at popular beaches where bathing is encouraged and facilities are provided for them. However, a section of river can also be designated as a bathing water if evidence can be provided that it attracts a large number of bathers.

Anyone can apply for designation, although it is usually the local authority. The application process is slightly different in each of the four nations, but all require evidence of the number of people using the site, information about facilities there and evidence of consultation with local residents, landowners and other stakeholders.

Applications can also be made to de-designate a bathing water site. Again, this is based on low numbers of people swimming rather than water quality.

As a result of being designated, every bathing water must be tested regularly throughout the bathing season and is given a classification based on its quality: ‘excellent’, ‘good’, ‘sufficient’ or ‘poor’.

However, it is important to note that these are not the same classifications as those in the Water Framework Directive. Under the WFD, a river is classified with regard to its chemical quality (ammonia, phosphate, temperature, pH, chemicals, metals), biological quality (invertebrates, fish, plants) and physical condition. Under the Bathing Water Directive, designated bathing waters are classified using different parameters, which measure the concentration of faecal indicator organisms (bacteria) found in the water.

The standards used to assess river water quality, for example for fish and invertebrates, do not include bacterial indicators as these have little effect on those organisms. It is therefore possible that a river might receive a ‘good’ or ‘high’ classification for the WFD but not meet the required standard for bathing water.

Under the BWD, water is tested for two types of bacteria that are known to cause stomach upsets and diarrhoea, and can have even more serious health consequences: escherichia coli (E. coli) and intestinal enterococci. The water’s category is based on the levels of these bacteria, measured through samples from the past four years (or the data available if the designation has not been in place for that long). Different criteria are used for the categories depending on whether the site is a coastal or inland bathing water. The thresholds are given in the table below.

By law, the local council must display information online and on signs at the site about water quality and pollution sources during the bathing season. If there is a temporary pollution incident – for example, a discharge of untreated sewage or chemicals into the river – it must explain the nature of the problem and how long it is likely to last.

If a bathing water is classified as ‘poor’, an ‘advice against bathing’ symbol must be put up at the site and online, along with information about pollution sources and what action is being taken to clean it up. This does not mean people cannot swim at the site, but there might be an increased risk of getting ill.

E. coli and intestinal enterococci get into water from the following sources:

Bacteria in rivers can come from multiple sources and may appear at a bathing site having entered the river some way upstream.

Sun Yan Evans, technical director and flood risk practice leader at engineering consultancy Mott MacDonald, says regular and accurate collection and analysis of samples is essential to find all of the sources and to understand how and when they contribute to the overall level of bacteria at any location. “Data is king,” she says. “You have to monitor the water to know what is in it and where it has come from, and to inform which solutions will be most effective.”

The majority of the UK’s sewers are combined sewers, which carry both foul sewage from people’s houses and surface water from roofs and drains. This combined flow is carried through pipes to a treatment works, where it is treated and the effluent discharged into the local watercourse.

In heavy rainfall, the volume of surface water increases and the combined sewer can become overloaded. To prevent sewage backing up pipes and flooding people’s homes and gardens, storm overflows, or outfalls, are incorporated into the sewerage network. These outfalls discharge the untreated flow of foul and surface water directly into rivers until the emergency is over and the flow is reduced to a level that the network and treatment works can cope with. The network may also include emergency overflow outfalls that discharge sewage in rare events such as a pump failure or blockage in the sewerage system.

In recent years, recordings have shown an increase in the number of times water companies have discharged untreated sewage into rivers at treatment works or at emergency/storm outfalls. Reasons for this include:

1. Climate change
   Sudden heavy rainfall events are increasing as a result of climate change. These events can overload drainage and sewerage systems very quickly.
2. Population growth
   As the population increases, so does the amount of water consumed and the amount of sewage that needs to go through treatment works. There are now 27 million more people living in the UK than when the Victorian sewers were built.
3. Increased water usage
   The average person in the UK uses 149 litres of water a day. Since 1975 the amount of water used by UK households has risen by 70%, owing to appliances such as dishwashers and washing machines, which use a large amount of water; people taking showers more often; and washing cars.
4. More hard surfaces
   Every road, car park, roof and paved area collects rainwater that would otherwise soak into the ground. This water runs off into drains, which are often connected to the combined sewers. The problem is exacerbated by people paving over their front gardens to create parking spaces.

The Rivers Trust has produced a map to show where the sewerage network discharges treated effluent and overflows of untreated effluent and storm water into rivers in England and Wales – explore it below.

Effective solutions to poor water quality require a catchment-wide approach that clearly identifies all of the factors contributing to the issue and analyses the impact, cost and carbon contribution of any potential intervention, as well as any societal benefits. 

The most expensive and carbon-intensive solutions are those that require significant new hard infrastructure (known as ‘grey’ solutions), such as adding settlement tanks at treatment works, or additional chemical treatment. Intervening earlier to reduce the volume reaching the treatment works and outfalls can minimise the need for grey solutions.

Options that use natural elements (known as ‘blue’ or ‘green’), such as sustainable drainage and reed beds, are often cheaper and far less carbon intensive, and can provide additional social benefits. ‘Grey’, ‘blue’ and ‘green’ solutions often complement each other, and a combination of all three working in harmony may offer the best overall outcome.

Solutions fall into three categories:

1. Managing the flow of water into the river from hillsides through the river basin catchment (rural environment)
2. Managing the flow generated within the urban environment
3. Treating the flow before it enters the river (at outfalls and treatment works)

Managing the flow of water into rivers from hillsides along a catchment can be achieved predominantly by ‘blue-green’, or natural management, techniques including planting and installing sustainable drainage. Vegetation can slow the flow of water and improve the soil, so more water is trapped on the hillside and does not reach the river in the valley and urban settlements below.

This approach is being adopted by Dŵr Cymru Welsh Water as it aims to reduce pressure on its wastewater networks and improve the performance of combined sewer overflows (CSOs). Under the UK-wide 21st Century Drainage Programme, the organisation has initiated the Storm Overflow Assessment Framework (SOAF) programme to improve the highest priority storm overflows.  

Stephen Ollier, a senior water engineer at consultancy Arup, describes one of the projects on the programme: “It is a small town in a valley with marginal, bare, grazed and compacted hillsides on both sides. When it rains, water flows unabated down the hills and overloads the combined system at the urban/rural boundary. This volume of water is too great for the traditional below ground pipe network, leading to frequent storm overflows from the wastewater network.”

A traditional approach would be to store the excess flow within the network, but this would have been a high cost, high carbon solution, due to the need for large, deep, concrete storage facilities with associated pumping. The better, greener solution, Ollier says, was to manage the water on the hillside by regenerating the ecosystem that was there previously – planting vegetation to trap and slow down the flow of water and improve the soil.

This approach can be combined with the construction of naturalised channels, dams and other natural flood management (NFM) solutions and regenerative land management (RLM) techniques on the hillside and in the valley bottom to further contain, manage, and divert the rural run-off before it gets into the adjacent sewer network. “Solutions can and should start right where the rainwater first meets the ground, using nature to manage and create value from water,” he says.

Where river catchments pass through farmland, water quality can be affected by agricultural practices. For example, in some places cattle stand in rivers to drink and cool down, which inevitably results in cattle faeces getting into the water. While this could be managed by fencing, it requires careful negotiation as it is likely to be a well-established practice.

Other pollutants, including chemicals from fertilisers, pesticides and bacteria from livestock faeces, get into the river from run-off from fields during heavy rain. Tim Harris, director of consultancy TH Environmental, says farmers can invest in relatively inexpensive, small-scale engineered solutions to reduce run-off, including natural flood management solutions such as swales and ditches. “If you hold back farm run-off, that prevents faecal matter going into the river and the bacteria dies off,” he says. “It doesn’t have to be difficult or expensive.”

A move towards more regenerative farming techniques, working to revitalise the soil and the environment, could also have a positive impact on water quality. park, with potentially disastrous consequences for the downstream river and urban drainage systems. But if the soil is well-managed and healthy, there is more potential for faecal matter from livestock to be absorbed into the soil and degraded naturally rather than being washed away in the next storm.

Managing the flow of water in an urban environment is difficult when a town’s sewerage network is based on Victorian combined sewers designed for far lower flows. Still, solutions are available, starting with encouraging consumers to lower their water consumption and recycle grey water.

De-combining storm and foul sewers would dramatically cut the volume of flow to treatment works but would be an impossibly expensive option on a nationwide scale. However, there are places where it may be possible at local level. For example, some housing estates built in the past century have separate systems but these are combined once they reach the adopted highway. In some circumstances they could be de-combined and the storm water diverted through a sustainable drainage (SuDS) process to the nearest watercourse. De-combining not only improves urban drainage but can also provide wider benefits for communities, such as amenity provision, health and wellbeing, urban cooling, air quality and carbon sequestration.

Many new housing developments now incorporate some form of natural drainage system or green infrastructure to handle surface water run-off, such as swales and ponds that hold water during high rainfall, then either release it into the ground or through the combined sewer system once the volume has dropped. Retrofitting these features in urban areas could capture significant volumes of run-off during heavy rain to prevent it from overloading the network and treatment works.

There are circumstances in which the best solution is to treat the flow just before it goes into the river. In this situation, the most common is ultraviolet (UV) light. UV radiation kills bacteria, as well as some viruses, algae and fungi, by destroying the DNA of the microorganisms. However, it is an expensive and carbon-intensive process.

Again, natural solutions can be used if the space is available, such as planting reed beds to capture and clean the effluent as it heads towards an outfall. “Nature-based treatment of storm overflows can be a good solution in the right place, especially if surface water separation from foul is difficult and high cost,” Ollier says. 

He adds: “The natural treatment system means the CSO effectively becomes a mini, decentralised treatment works. At the same time you can create a wetlands area that becomes a local biodiversity hotspot and amenity facility, which is a great way to engage with local communities and help them be a part of the solution. Local storm water systems, including highway drainage, which carry a range of pollutants, can also be diverted into these wetlands for wider treatment benefits.” 

This solution is another element in the nature-based solution toolbox that could be adopted across the UK at suitable sites.

Engineers have a pivotal role to play in ensuring that rivers are clean enough both for bathing and to protect and improve the biodiverse flora and fauna that rely on them for habitat. But the solutions required are likely to be more imaginative and diverse than simply building more treatment works or adding extra chemical processes. The complex interaction of pollutants and their route into rivers demands a catchment-wide approach, with data and modelling helping to identify the most cost-effective, lowest-carbon solutions that give the widest combination of benefits.