Scotland and lochs are synonymous. Those huge deep primordial stretches of water that divide the land, reflect the hillsides and sparkle in the sun characterise who we are, and how we are perceived, at home and abroad.

They are famous across the world for their beauty, their grandeur and their mystery. They are marketed as pristine and pure, and attract thousands of tourists to boost Scotland’s economy.

It comes as something as a shock, then, to learn that an astonishing 45 lochs have been polluted in breach of environmental safety limits over the last ten years. The pollution comes from the toxic chemicals used by fish farms to kill the lice that plague caged salmon. The chemicals are also a risk to human health.

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This is not how it should be. If environmental quality standards are set, they should be met and enforced, not ignored. Otherwise wildlife will suffer, and public health could be put at risk.

Unfortunately, however, the Scottish Environment Protection Agency (Sepa) is coming under fire - yet again - for not doing its job. Part of its remit these days is to help economic growth, and there are plans to double the size of the fish farming industry by 2030.

That now looks both unsustainable, and unwise. Instead of promoting such growth Sepa and Scottish government ministers should be thinking about how to curb pollution by limiting the size, stocking density and locations of fish farms.

Of course the industry brings its own economic benefits, but these should not be at the expense of one of Scotland’s most precious assets – our beautiful environment.