Norfolk Broads toxic algae warning
Anglers fear a build up of toxic algae in the Norfolk Broads could put off holiday makers.
The Environment Agency has relocated more than 500,000 "suffocating" fish since March, because of the oxygen-depleting Prymnesium algae bloom.
Angling trust regional chairman Kelvin Allen said as temperatures rise over the summer "the smell of dead fish could become quite unpleasant".
The Broads Authority said "only a tiny part" of the waters were affected.
Mr Allen said: "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."
A spokesman for the Broads Authority, which manages the National Park, said: "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."
He added the authority was working with specialist laboratories in France and the UK to develop better testing techniques to find the best approach to tacking the issue.
An Environment Agency Spokesman said: "We continue to work around the clock to monitor the situation".
The algae bloom is being attributed to a mixture of environmental conditions, including rising water temperatures.
The last similar occurrence was in Hickling Broad in 2012, when 35,000 fish were rescued and relocated.