A devastating pollution incident has wiped out a significant number of fish, eels, and birds in the Knockando burn, a tributary of the River Spey in Moray.
A chemical, thought to be caustic soda, is understood to have entered the water, "destroying" various species in recent days.
The Scottish Environment Protection Agency (Sepa) is investigating the potential pollution. Fly fishers warn the burn's salmon population has been "wiped out" and could take years to recover.
Duncan Ferguson, director of the Spey Fishery Board, said the pollution incident was one of the largest he had seen in 36 years of working on the river, with a two-kilometre stretch of the Knockando burn affected.
He said: “It’s a tragic event.
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“It’s a really bad outcome and it didn’t have to happen.”
He said the salmon population could face a five-year period of recovery, with a two-kilometre stretch of the burn “destroyed”.
The chemical is thought to be industrially linked, he said.
The pollution incident comes at the peak period for fly fishing on the Spey, and just 10 days after another pollution incident at Spey tributary.
Earlier, a number of salmon died after white paint was spilled into the Burn of Carron.
A spokesman for Sepa said: “Sepa are investigating a potential pollution incident in a tributary of the River Spey and are working to identify the source and impacts.”