A salmon farming company with a factory in Fife is under investigation for possible misreporting of chemical use.
Mowi, formerly known as Marine Harvest, is among a number of firms being probed by the Scottish Environment Protection Agency (Sepa).
The Norwegian-owned company has a plant in Rosyth.
Farmed salmon are treated with chemicals to ward off disease and infestations such as sea lice but there are limits on how much can be used.
Widely-used chemicals include hydrogen peroxide baths and the pesticide emamectin benzoate, which is put in fish feed.
There are concerns that the substances could be damaging the environment in some of Scotland’s lochs, along with faeces and food waste coming from thousands of salmon in fish farm nets.
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Mowi has denied any wrongdoing and said it used medications sparingly.
The company, which produces up to 60,000 tonnes of salmon each year in the UK alone, said it had confidence in the numbers it had provided on medication use and that it was supporting regulators with a six-month audit.
The allegations were revealed on Monday night by the BBC’s Panorama programme , which said Sepa’s enforcement team removed documents during an inspection of Mowi’s UK head office in Fort William earlier this month.
Terry A’Hearn, chief executive of Sepa, said: “If companies do the right thing, then they have nothing to worry about.
“If companies do the wrong thing, we’re there to find that out and make sure they improve their game.
“If that’s going to take tough action, you can be assured we’ll take it.”
A Sepa spokesperson said the agency had advised Mowi Ltd of an audit at Stob Ban, Fort William on April 23 2019.
“Mowi was subject to an unexpected inspection…on May 1 2019 and a further announced inspection on May 7 to obtain further information,” the spokesperson added.
“Sepa is unable to comment further on its current audit and unannounced inspection programme under way at present.”
The industry says salmon farming is a sustainable way to produce food and provide jobs in remote rural areas.
Ian Roberts of Mowi said: “I wouldn’t be doing this if I thought that we had a strong negative impact on the environment.
“It is farming at the end of the day so, no matter what you’re farming, you have some level of impact.
“We also need to manage these local impacts around the farms.”
Earlier this year it was reported that the Rosyth plant had been probed as part of a European Commission investigation into alleged illegal cartels.
Officials carried out unannounced inspections at Mowi, along with other Norwegian-owned companies, in February.
The investigation is believed to focus on alleged anti-competitive business practices such as price-fixing.
At the time, Mowi said there was no basis for the inspection and the probe was “surprising”.