With their pretty villages and miles of waterways, the Norfolk Broads attract a million tourists each year, but there are fears the smell of dead fish could be getting up visitors' noses.
While recent temperatures topping 20C (68F) have attracted the first holidaymakers of the season to the area, the pleasant weather could have the unfortunate side effect of increasing a build up of toxic algai which depletes oxygen levels in the water and kills fish.
Environment Agency (EA) workers have recently been forced to relocate more than half a million fish and are carrying out daily monitoring after anglers spotted carcasses floating in some waterways, including Hickling Broad near Potter Heigham. WORDS: PA.
If the forecast warm weather continues, this could increase the bloom, meaning the figure could reach more than one million, a spokesman said.
Anglers have warned the rising numbers of dead perch and bream could put off visitors to the National Park - previously re-branded as Britain's Magical Waterland - and have a knock-on effect on biodiversity.
Bosses at the Broads Authority, which manages the area, have said they are working hard with the EA to find a solution - adding that the problem should not put off visitors as it was confined to small areas.
He said: "Our members first noticed fish behaving strangely around Christmas - they were moving from their normal locations and weren't interested in food.
"Obviously, this is of concern to anglers but it also has further reaching implications.
"If you take into account the birds which feed on the fish and the wider food chain, this could have serious consequences to the natural environment."
The algai bloom has been attributed to a mixture of environmental conditions, including salinity and water temperature.
It is not known what has caused these conditions to alter so dramatically, but Mr Allen said dredging and land drainage could be factors.
He said there needed to be a coordinated response to bring together groups such as anglers, farmers and tourism businesses to find a solution.
"The Broads are the UK's largest inland fishery and 18% of visitors take part in angling at some point during their visit," he added.
"People come here to enjoy nature and the outdoors.
"If we don't protect the natural environment, we could lose the very thing that makes it special.
"Apart from anything else, as temperatures start to rise in summer, the smell of dead fish could become quite unpleasant."
A Broad Authority spokesman said: "Huge numbers of visitors are enjoying the Broads during the current spell of great weather and will continue to throughout the season and beyond.
Kelvin Allen, eastern region chairman of the Angling Trust
"The fish issue is confined to a tiny part of the waters and once whatever water conditions are causing it have resolved, numbers will naturally recover."
The EA rescued and relocated 230,000 fish last month after they were found shoaling in a shallow haven away from the bloom near Potter Heigham.
A further 110,000 have recently been moved from Somerton, roughly six miles away, and over the weekend another 300,000 fish were moved.
Once transported a sufficient distance from the bloom, the fish are able to swim freely into surrounding rivers.
The last similar occurrence in Hickling Broad was in 2012 when 35,000 fish were rescued and relocated.
An EA spokesman said: "Our teams have taken action to rescue and relocate more than half a million fish in the Norfolk Broads which were in danger of suffocating due to the effects of a Prymnesium algai bloom.
"We are continuing to work around the clock to monitor the situation. "
Dan Hoare, from the Broads Authority, said it was working with specialist laboratories in France and the UK to develop better testing techniques to find the best approach to tackling the issue.
He added: "We understand the public concern and the impact this is having and are doing everything we can to support and facilitate the Environment Agency, as the organisation responsible for fish welfare and events which affect it, in monitoring and resolving the situation."
Anyone who sees dead or distressed fish should contact the EA hotline on 0800 807060.
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