Buckinghamshire Council has responded after a number of dead birds have been found in the Spade Oak Nature Reserve.
The council-owned reserve sits in Little Marlow with the first death reported on social media on August 21.
Wild Marlow has since said that there has been a 'huge death toll' in wildlife in recent weeks with one resident sharing an image of a dead mute swan on social media.
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The Department for Environment, Food and Rural Affairs (DEFRA) has carried out tests in the area and confirmed no evidence of bird flu has been found.
It is now thought that the deaths are due to another type of avian virus but no tests as of yet confirm this.
A council spokesman has advised people not to let their dogs go into the water and any dead animals seen to be reported so it can be collected properly.
John Chilver, Cabinet Member for Finance, Resources, Property & Assets said: "We are in the process of arranging water testing and are in contact with the UK Centre for Ecology & Hydrology, who yesterday reported on Radio 4, concern about bird deaths elsewhere thought to be as a result of toxins in fish, related to algae.
“We will continue to monitor the situation and notify the relevant authorities should the situation persist or escalate.”
A Wild Marlow spokesman said: "We have never seen such high numbers at the location previously and we need to know the cause so that action can be taken to prevent further deaths.
"This beautiful jewel in the crown of the Little Marlow Lakes Country Park, is an incredibly important site for wildlife, biodiversity and human health.
"We really hope appropriate action is taken to safeguard the future of this Nature Reserve.”
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