Thousands of farmed salmon are understood to have died following an algae outbreak on Loch Fyne.
The Scottish Salmon Company, which runs the farm at Quarry Point, says it believes the problem was caused by the recent warmer weather.
It would not confirm the number of fish affected, although local observers described it as a significant figure.
Lorries have spent the day removing what is believed to be hundreds of tonnes of dead fish for disposal.
The matter has been referred to Marine Scotland.
A spokesperson for The Scottish Salmon Company said: "Following the warmer water temperatures in recent weeks, a suspected algae bloom was reported in Upper Loch Fyne.
"Naturally occurring biological challenges such as these are unavoidable and we take rigorous steps to protect our livestock.
"The health and welfare of our fish is at the heart of our operations and, in line with standard procedure, the matter has been reported to Marine Scotland."
A Scottish government spokesperson said: "Marine Scotland's Fish Health Inspectorate was made aware of a loss of salmon by the Scottish Salmon Company last week and are currently liaising with the company."