Over the first eight months of 2020 the average number of monthly water samples taken by the Environment Agency was 2,837, according to data obtained by the civil society group Unchecked UK and analysed by ENDS.
This is two thirds lower than the monthly average of 8,336 recorded during 2019.
The average monthly number of tests for individual measures of water quality also declined over the period falling 61% from 172,281 in 2019 to 66,818 over the first eight months of 2020.
Environmental groups and legal experts believe that the lack of testing during the pandemic means that pollution incidents are more likely to have gone unnoticed and polluters are less likely to face consequences for their actions.
“There is no excuse for this sudden drop in testing,” said Nick Measham, the chief executive of the campaign group Salmon and Trout Conservation.
“A lot of other people that have essential jobs have carried on going out and doing their jobs during the pandemic.
“You could argue that collecting water samples where there are no other people around is not a high-risk activity.”
The rapid decline in testing over 2020 comes after a long-term decline in testing over a period several years.
In 2013, a total of 159,964 water samples were taken by the Environment Agency, compared to 100,037 in 2019, according to the data, which was obtained using freedom of information legislation.
“We are particularly concerned that the amount of monitoring being done by the Environment Agency is declining,” said Measham.
“If you are not out there testing there are going to be pollution incidents that go unnoticed and potential polluters will benefit from that.
“Because Environment Agency resources are under massive pressure, they are having to allocate them in ways that don’t continue to protect the environment in a way that the public would be led to believe or expect.”
An Environment Agency spokesperson said: “We have continued to monitor water pollution throughout the pandemic, and most importantly responded to each and every incident reported to us.
“Some of our monitoring activities were reduced in order to ensure we kept our staff safe, however advice continued to be given remotely – and as we recover we expect to see our monitoring return to full capacity.
“Environment Agency staff respond to pollution incidents 24/7 – working across the country to safeguard our environment, contain pollution and protect water quality.”
Previously the Environment Agency has said that it has continued to work to tackle illegal and environmentally damaging operations throughout the pandemic – taking proportionate enforcement action to bring businesses back into compliance and to prevent and disrupt criminal activity.
Water quality testing on coastal waters and lakes in England completely stopped in May 2020, due to the coronavirus pandemic before resuming in July 2020.
The latest information about the decline in testing comes amid increasing concerns about pollution discharges into British waterways.
Earlier this month a BBC Panorama investigation revealed that water companies have been discharging untreated wastewater into rivers in breach of their permits on a regular basis.
The firms are only allowed to discharge raw sewage into rivers and seas if there has been exceptionally heavy rain and only if the company in question has already treated a specified volume of water, but the Panorama team found that many were discharging frequently and for long periods of time without any of these conditions being met.
Of 10 companies investigated by Panorama, seven had treatment works that were breaching their permits.
Welsh Water was found to be one of the worst offenders with its Aberbaiden plant illegally dumping sewage into the protected river Usk for 12 consecutive days in December.
Much of the dumping goes unreported, despite the sector being obliged to report their combined sewer overflow (CSO) discharges, known as event duration monitoring, to the Environment Agency.
In 2020, the sector told the agency it dumped sewage into England’s waters 400,000 times, up from 200,000 the previous year, for a total of 3.1 million hours.
The actual figures are believed to be much higher.
Hundreds of CSOs are being investigated for the frequency of their sewage spills, according to ENDS' analysis of the water industry national environment programme (WINEP), but it will be some years before any action is taken.
The Environment Agency has been working with water firms to come up with the 2020-25 WINEP, which is estimated to cost around £4.6bn.
ENDS analysis of the programme coupled with data from a freedom of information request shows that 727 CSOs need to be investigated for the frequency of their spills.