Anglian Water has pulled the plug on access to its leisure areas - including Grafham Water - in a bid to reduce the spread of coronavirus.
The Huntingdon-based business had hoped to keep its “water parks” open but decided to put them into lockdown to protect members of the public and staff.
It is now trying to work out how to make refunds to its customers who have paid in advance for fishing season tickets, parking permits and other events.
Reservoirs like Grafham are hugely popular visitor attractions during the summer, with grounds around the lake providing a wide range of recreational activities like walking, cycling and birdspotting as well as hosting major venues for fishing and sailing which bring thousands of people to the district.
But Jake Williams, head of parks and conservation at Anglian Water, said they had “sadly” made the decision to close the water parks to the public with immediate effect.
“We had hoped to keep our green spaces open, but the wellbeing and safety of our customers, visitors and colleagues is the most important thing at this time,” he said.
“All events at our parks will be cancelled until the beginning of June and the Anglian Water Music Festival will be postponed until next year. We will be reviewing this on a three-month basis as current advice is updated.”
Mr Williams said: “We recognise that some people may really struggle financially during these uncertain times. For our visitors, who have fishing season tickets, parking permits or festival tickets, we are working to find solutions to address this.
“Please bear with us, as we want to ensure any changes or refunds can be processed as easily as possible. We will be in touch with you as soon as we can with further details.”
He added: “We would encourage everybody to follow the Government’s advice to social distance and not travel wherever possible to protect the most vulnerable in our communities.”
The music festival was to have taken place at Rutland Water in June and the bill included Scouting for Girls and the Hoosiers.
Anglian Water supplies drinking water to 4.3 million customers and treats used water from six million.