De-icing fluid sprayed onto aircraft at Edinburgh Airport is leaking into the River Almond and harming fish, watchdogs say.
The fluid is sprayed onto aircraft before they take off during winter, with around 150 litres thought to be used each time.
The Forth Rivers Trust told BBC Scotland de-icer was entering the river via the Gogar Burn, which flows under the airport. This can affect salmon, trout and eels in the area.
In October last year, the issue is understood to have caused a build-up of fungus along 2.5 miles of the river.
The Scottish Environmental Protection Agency (Sepa) issued the airport with an enforcement notice last year.
Alison Baker, the Trust's director, told the BBC: "The constituents of de-icer, glycols and urea will cause stress to pollution-intolerant fish and invertebrates; these will be our native fish populations predominantly, such as salmon, trout and eels.
"This issue has been raised with Sepa in the past and we are disappointed that this matter is still non-compliant, particularly as we and others are working hard to restore the River Almond for communities and wildlife."
Edinburgh Airport said it had invested in new equipment to pre
A spokesman said: "De-icing is a core part of aviation in the winter months and is required to maintain the safety and integrity of aircraft.
"As an airport, the safety of passengers and staff is paramount to our operations and, like all businesses in winter, de-icing is required for operational safety, something we work with our business partners to responsibly manage.
"We have made significant investments in machinery and infrastructure to reduce the impact of these activities on the Gogar Burn and we will continue to work closely with our environmental regulator Sepa on further improvements in this area.
"We welcome comments from the Forth Rivers Trust that there have been improvements made and that all businesses need to further action."
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