ONE fish farm produces the same amount of waste as all of Scotland’s west coast towns put together, an expert has said.

Dr Richard Luxmoore, senior nature conservation adviser at the National Trust for Scotland, said a moderately-sized farm dumped the same amount of sewage as a town twice the size of Oban.

It comes as a string of experts warned salmon farming was having a deadly impact on the environment.

Dr Luxmoore said fish farms were pumping “huge quantities” of organic waste into the sea, making up around 80 per cent of all sewage.

He told a Holyrood committee: “A single fish farm, which currently has a maximum size at the moment of 2,500 tonnes, produces the sewage equivalent of a town twice the size of Oban.

“So if you added up all of the towns on the west coast, virtually, they are producing the same amount of sewage as one fish farm – a moderately large fish farm.

“Now of course, you’re not allowed to discharge waste from a single septic tank into the sea without it being treated.

“And if you were to suggest building two Obans somewhere in the Sound of Mull, saying, ‘Is it alright if we just chuck the sewage straight in the sea?’, you would get very short shrift over it.

“But somehow putting a new fish farm in seems to be exempt from a lot of these issues.”

He said there was little regulation over the deadly chemicals used by fish farms – with some, including hydrogen peroxide, used in increasing quantities.

Meanwhile, the number of fish dying on the farms has been “inexorably rising over the last four or five years”.

Dr Luxmoore said a range of diseases were to blame, but the figures showed the industry was struggling to control the issue.

Gill disease was listed as a major cause of fish deaths, as well as new mechanical treatments for sea lice.

Jon Gibb, of the Lochaber District Salmon Fishery Board, said mystery diseases in wild fish had led to “rivers full of dead fish”.

He said fish farms and other “aquaculture” were not the main culprit, but were “most certainly adding an extra pressure to already threatened stocks”.

He insisted studies had shown marine survival rates were “extremely poor” on parts of the west coast.

“You actually now have rivers that could simply be classed as extinct of Atlantic salmon,” he added.