Lobsters, crabs, clams and oysters are the “forgotten victims” of sewage being dumped into the sea and rivers around the UK, new analysis has shown.

Waters containing shellfish were dumped in nearly 29,000 times last year, with the longest event lasting 5,000 hours.

The research by the Liberal Democrats found 207,013 hours worth of sewage were dumped in waters around England inhabited by shellfish in 2021 alone.

South West, Southern Water and Anglian Water were reportedly the utilities companies with the worst records.

Tim Farron, the Lib Dems’ environment spokesman, said: “England’s treasured shellfish, our prawn, crayfish, lobsters and crabs, are the forgotten victims of this environmental scandal.

“The past week we’ve seen our beaches closed because of these polluting water companies. All the while, they are raking in billions of pounds in profits and forking out eye-watering bonuses to their CEOs. Frankly, the whole thing stinks.

“Why aren’t Government ministers listening to the public on this? They are ignoring the country’s outrage at this scandal.”

The opposition party claimed the longest sewage “dump event” into shellfish water last year took place at Morecambe Bay by United Utilities, lasting 5,000 hours.

But the Lib Dems believe the sewage monitor at the site only worked 15% of the time, suggesting that figure could be much higher.

In Sussex, Southern Water dumped sewage into Chichester Harbour for 4,996 hours in one overflow.

At the other end of the south coast of England, South West Water dumped sewage into the sea at Exmouth beach, which also contains shellfish, for 1,128 hours from just one overflow.

The Lib Dems have called for a sewage tax on water companies, in order to create a fund aimed at preventing sewage from polluting rivers in future.

Last week, analysis by the party revealed that bosses at Britain’s water companies have on average been granted a 20% total pay rise in the last year, including bonuses, despite the rising number of incidents of sewage being pumped into open water.

David Jarrad, chief executive of the Shellfish Association of Great Britain, said that sewage being pumped into the sea could lead to a “lack of trust in consumption of shellfish by the consumer” and “short-term closures of areas where… oysters, mussels, clams are allowed to harvested”.

Mr Jarrad told the PA News Agency: “The way we classify our waters around the UK coast, you only need to have two bad readings in the year and you will be downgraded for 12 months the following year.

“These pollution events today could be impacting on the sales of that product in 2023.”

While Mr Jarrad said sewage could “potentially” impact the breeding of lobsters and crabs, it was shellfish such as oysters and mussels that were most at risk.

“It is the filter feeders that are filtering the water that potentially has bacteria or viruses in it from the sewage, that is where the problem lies,” he said.

A spokesman for Water UK, which represents the water companies, said they agreed there is an “urgent need for action to tackle the harm caused to the environment by spills from storm overflows and wastewater treatment works” and are investing in £3 billion of improvements.

The spokesman added: “However, companies want to go further, faster and are pushing to be able to spend more, and for processes to be streamlined so that investment can be quickly targeted where it is needed most.

“Any new investment must be combined with action from Government on wet wipes and urban creep that are increasingly triggering spills.”

The Government said it expects the water companies to take further action to reduce pollution.

“We have been clear that the failure of water companies to adequately reduce sewage discharges is completely unacceptable,” a Downing Street spokeswoman said on Monday.

“They have a duty to put their customers before shareholders and we would expect them to take urgent action on this issue or face fines.”