Livestock farms in England polluted rivers 300 times last year, causing 20 major incidents, according to the latest government figures.
Yet only six farms were prosecuted in 2021, with the Environment Agency handing out warning letters instead.
The dairy industry – mainly thanks to the waste produced by its millions of cows – is the worst environmental offender, linked to half of all agricultural pollution.
The government has said prosecution is a last resort for repeat offenders.
The National Farmers Union (NFU) said all farmers take their environmental responsibilities seriously and are taking “voluntary action through industry-led initiatives to make improvements that benefit the aquatic environment”.
Much of the environmental threat to rivers from agriculture comes from cow waste called slurry – a mixture of manure and water that farmers store and spread as fertilizer.
Each of the UK’s 2.6 million dairy cows produces up to 53 liters of manure a day. That’s around 50 billion liters of manure a year – enough to fill Wembley Stadium more than 12 times.
The slurry produced must be stored but it can run off from poorly maintained containers or, if it is applied too much to the land or if it rains a lot, it can run off the fields.
Serious pollution incidents can result in prosecution.
One of the offenders is Michael Aylesbury, director of Cross Keys Farms Ltd. In June this year he was ordered to pay over £25,000 for polluting the River Frome in Somerset with slurry in 2020.
He had already been prosecuted for polluting the same stretch of the Frome in 2016, an incident that killed more than 1,700 fish.
Sue Everett lives by the river and filmed the most recent event in 2020.
“The first thing was the smell – it was terrible,” she said. “As I approached the river, I could see it was dark. The next morning I went out with my camera and took videos of the dead fish.”
She fears the public is unaware of the threat agricultural slurry poses to rivers, saying: “I think agricultural pollution has been hidden for far too long.”
But the government, farmers and the dairy industry say they are all taking action to tackle slurry pollution in rivers.
Kate Hoare, based near Saltash in Cornwall, is one of the farmers leading the way.
Not only does she carefully manage her slurry, but she has installed one of the UK’s first covered slurry lagoons which can capture methane gas to use to fuel her tractor.
She describes slurry as “liquid gold” and says every farmer knows the value of keeping it on the land and out of the rivers.
“It helps the soil, and it helps the grass, and it helps the cows produce the milk that we need to sell,” she said.
“So I think that’s at the forefront of every dairy farmer’s mind – how they can improve their slurry store and prevent it from filling up with rainwater and get the most out of this product.
“Because we’re all good at recycling, as you know. That’s what we do as farmers.”
To ensure best practice, farms are inspected by the Environment Agency. In 2021, 721 inspections were carried out on 693 farms.
More than half of the inspections revealed that the farmers violated the regulations governing the storage of liquid manure.
Freshwater fish conservation group Wildfish is currently suing the government over its treatment of water companies that pump sewage into rivers and seas.
But its managing director Nick Measham is also concerned about the threat posed by dairy farming and the slurry it produces.
He said: “More and more we are seeing across the country industrial scale agricultural units, particularly dairy and beef units. The manure they produce has to go somewhere.
“Frequently, farmers think of the river as an open sewer. This sludge is a really potent substance. I mean, it’s much more potent in terms of water impact than human sewage.”
“They have increased the number of agricultural inspectors, but until a few years ago the probability that you as a farmer would be inspected was about one in 200 years. So it is clear that this isn’t much incentive to clean up your act.”
The Environment Agency said it was working ‘constructively’ with farmers to reduce water pollution and had increased the number of inspections to more than 3,000 since January this year .
He added that since April 2021, he had issued at least 140 warning letters and demanded 6,169 improvement actions in farms, of which 2,791 were carried out.
He said he was focusing on “high-risk locations, previously non-compliant businesses and agricultural sectors of greatest concern”.
But he admitted that only six farm prosecutions had taken place in 2021/22, saying the legal action was being used as “a last resort in the event of persistent non-compliance”.
Defra said it had doubled funding for its Catchment Sensitive Farming program, which provides free advice to farmers to help them better manage manure and soils.
And, earlier this month, it made available a £13million slurry infrastructure grant for farmers to improve their storage.
The NFU hailed the funding, saying farmers had already reduced serious pollution incidents year-on-year by 75% compared to 2000.
NFU Vice-Chairman Tom Bradshaw said: “The NFU will continue to work with Defra and the Environment Agency through their infringement advisory approach, to effectively communicate agricultural rules for directing water to its members.”
Meanwhile, the UK’s biggest dairy company, Arla, said it was now paying its farmers to work in a more environmentally friendly way.
A spokeswoman said: “Our farmer owners are rewarded with the price of milk for covering slurry stores, using certain slurry spreading techniques, and using slurry to make biogas, a type of renewable energy that can be used to generate electricity and power vehicles.”