How much raw sewage is released into rivers and the sea, and what are the rules?
Every major English water company has reported data suggesting they've discharged raw sewage when the weather is dry - a practice which is potentially illegal.
Water companies can release untreated sewage into rivers and seas when it rains to prevent it flooding homes, but such spills are illegal when it's dry.
On dry days there is less dilution and sewage can cause more damage to the local environment and pose a health risk to swimmers.
How much sewage is released into the sea and rivers in England?
Sewage spills into England's rivers and seas by water companies more than doubled in 2023.
According to the Environment Agency, there were 3.6 million hours of spills, compared to 1.75 million hours in 2022.
Water UK, the industry body for sewerage companies, said this was "unacceptable", but argued that the record levels were due to heavy rain and increased data collection.
However, the Environment Agency said that increased rainfall does not override water companies' responsibility "to manage storm overflows in line with legal requirements".
Some environmental charities blame water companies for a failure to fix leaky pipes and other damaged infrastructure - and criticise the regulator for not forcing them to act.
Why is sewage released into the sea and rivers?
Most of the UK has a combined sewerage system, meaning that both rainwater and wastewater - from toilets, bathrooms and kitchens - are carried in the same pipes.
Wastewater is usually sent to a sewage treatment works.
But capacity can sometimes be exceeded during heavy rainfall, especially if dry ground cannot quickly absorb large quantities of water.
This could lead to inundation of sewage works and potential flooding of homes, roads and open spaces.
The system is therefore designed to overflow occasionally, and discharge excess wastewater into the sea and rivers.
This is called combined sewer overflows (CSOs).
However, according to the BBC there is evidence that some water companies are potentially spilling sewage when it is not raining.
Without rainwater to dilute the waste, this can lead to higher concentrations of sewage entering waterways - and is therefore illegal.
The BBC has examined spill data sent by the nine sewage companies from 2022 to the Environment Agency and cross-referenced it with rainwater. The results of the BBC's analysis suggest there may have been dry spills starting on more than 200 days in 2022 lasting over 29,000 hours - including during the record summer heatwave when people were cooling off in England's rivers and seas.
To confirm this has happened the Environment Agency says they carry out further checks and visit the sites where the spills may have taken place.
The BBC also found that untreated sewage was illegally released into Lake Windermere in the Lake District in February 2024 after a fault.
Water companies which are found to have breached the rules by spilling on dry days or failing to meet other conditions can be fined or prosecuted.
What is being done to tackle sewage discharges?
In April 2023 the Conservative government announced a plan to improve water quality.
As part of this, it said polluters could face unlimited fines in the future which would be re-invested into a new Water Restoration Fund which aims to improve water quality.
Six months later Water UK, the industry body, announced plans on behalf of its members to almost double spending to pay for upgrades and cut sewage discharges.
It said this would be the "most ambitious modernisation of sewers since the Victorian era", but that customer bills would have to rise by £156 a year to cover the cost.
This week the UK's political parties released their manifestos including their proposals for the sewage industry.
Steve Reed, Shadow Secretary of State for Environment, Food and Rural Affairs told the BBC that a Labour government would "put the water companies under special measures to force them to clean up their act".
"We will give the regulator tough new powers to make law-breaking water bosses face criminal charges and ban the payment of their multi-million pound bonuses until they clean up their toxic filth," he added.
The Liberal Democrats have said they will introduce a sewage tax on water company targets and set legally binding targets to prevent sewage dumping bathing waters and "highly sensitive nature sites by 2030".
Sian Berry, parliamentary candidate for the Green Party told the BBC: "Private water companies have failed to invest, resulting in sewage leaks and run-off at record levels. It's made our coastlines and inland waterways filthy and unhealthy when they should be clean and safe."
The BBC has approached Reform for comment on this issue.
What are the health risks of swimming in polluted water?
In May 2024, a team of the UK's top engineers and scientists warned of the growing public health risk from human faeces in the country's rivers, and called for more regular testing.
The presence of faeces can expose people to bacteria such as salmonella and E.coli, which cause diarrhoea and vomiting, or viruses like hepatitis A which can lead to liver infection.
Also in May, thousands of residents in Devon were told to drink bottled water after their supply was contaminated with the cryptosporidium parasite - possibly as a result of a faulty valve on private land. Consumption of the parasite can cause prolonged diarrhoea.
How can I check if the sea near me is clean?
Every week between May and September, the Environment Agency measures the water quality at "bathing sites" across England, and in some places it issues daily pollution risk forecasts.
You can search its website by location. There are similar websites where you can find out about beaches and bathing water in Scotland, Wales or Northern Ireland.
But outside of these times and locations regularly testing for organisms carrying faecal-oral disease is not carried.
By the end of this year all water companies are expected to have maps showing near real-time discharges at their storm overflows to keep the public better informed.
How clean are UK waters overall?
Sewage spills have only been routinely monitored for a few years, so it is difficult to tell exactly how they have changed over time.
However, overall water quality has been monitored for decades. This also accounts for other sources of pollution, such as agriculture.
In May 2023, the Environment Agency said that 16% of assessed surface waters in England achieved "good" ecological status, including:
14% of rivers and lakes
19% of estuaries
45% of coastal waters
93% of designated bathing waters
Water quality is generally higher in other parts of the UK.
In Scotland, around two-thirds of surface waters are classed as having "good" ecological status.
In Wales the figure is 40%, and in Northern Ireland 31%.
