The number of incidents in which fish farms have polluted rivers and lochs has doubled in the last year, according to new figures from the Scottish Environment Protection Agency (Sepa).

The sharp rise in leaks, mishaps and complaints undermines claims by fish farmers that they are cleaning up their act. And it poses a problem for the incoming Scottish Executive, which has just backed an expansion of the aquaculture industry.

For anti-fish farm campaigners, though, the new figures are proof that pollution is getting worse. 'Salmon farms are a malignant cancer on the coast of Scotland and ought to be ripped out as a matter of urgency,' declared Don Staniford, of the Salmon Farm Protest Group.

Since 1996, there have been a total of 51 pollution incidents at fish farms. In every year until 2002, the number of incidents has been between five and seven. But in 2002-03, it leapt to 13.

Concentrated in the northwest, the incidents included leaks of fish sewage, fungi and oil. According to Sepa, one of the worst incidents, on the Morvern peninsula by the Sound of Mull in September, resulted in 'sewage fungus blanketing the River Rannoch'.

At Loch Erisort on the Isle of Lewis in August there were 'decaying salmon' floating in the loch after a net allegedly burst. While on the River Ailort, west of Fort William, in December, there were 'prominent fungal growths' and 'scum deposits'.

Incidents in previous years included 'grease heavily coating cages' in Loch Hourn, Knoydart; 'blood water leaking into the harbour' at Portree, Skye; and reports of sea lochs being 'turned red' near Tarbert, Harris. In November 2001, at Wharry Burn, Dunblane, there was a complaint about 'green foam' caused by the use of a cancer-causing chemical, malachite green, to clean fish cages.

The list of incidents and their descriptions was provided on request by Sepa to Staniford, an award-winning critic of the fish farm industry. 'The increasing scale of pollution incidents blows out of the water the claim that salmon farmers have cleaned up their act,' he said.

'Far from doing this, Scottish salmon farmers are redoubling their efforts to foul their own nest. These damning figures expose the industry's contempt for both the marine and freshwater environment.'

The events recorded were only the tip of the iceberg, Staniford argued. 'Incidents are so numerous that Sepa has lost track of them all and is now having difficulty in stemming the tide of pollution from factory fish farms,' he claimed.

'To tackle the problems posed by contaminated waste, toxic chemicals and illegal discharges of dead and diseased fish, Sepa must be given the resources to visit salmon farms more than once a year and carry out more random spot checks.'

Sepa said that it was not possible to attribute the increase in pollution incidents to one particular cause because the numbers were determined by a variety of factors. It also stressed that the information was not a complete historical record.

'Scotland has one of the toughest regulatory regimes for fish farming in Europe and we are continually improving our approach to this industry,' said a Sepa spokesman. 'Obviously, Sepa treats any breach of consent seriously, and we have a range of options for dealing with incidents, ranging from informal discussion to reports for the procurator fiscal.'

In the new partnership deal for government over the next four years, agreed last week by Labour and the Liberal Democrats, fish farming was given an unexpected boost. A promise was made to reduce the number of regulatory agencies that currently oversee the industry.

And the agreement said: 'We will support the growth of an aquaculture industry in salmon, other fin-fish and shellfish that is sustainable, diverse and competitive.'

This has been warmly welcomed by Scottish Quality Salmon (SQS), which represents most of the fish-farming industry. It argues that the industry has a tiny effect on the Scottish environment.

'The Sepa annual report reveals that fish farming has a minute impact on water pollution incidents -- representing less than 0.5% of the near 2000 incidents during 2001-2002,' said SQS chief executive, Brian Simpson.

'Furthermore, a recent independent study, carried out by the Scottish Association for Marine Science and Napier University concluded that the area of seabed affected by aquaculture is insignificant in terms of the total coastal resource.'

He added: 'The Scottish salmon farming industry is the most tightly regulated aquaculture industry in Europe. The industry is scrutinised by 10 different statutory bodies and subject to more than 60 pieces of legislation.'

Environmentalists, however, are worried about the backing the industry has been given by the partnership agreement. 'Scotland's salmon farming industry is not currently sustainable,' said Dr Dan Barlow, head of research at Friends of the Earth Scotland.

'The fact that pollution incidents have doubled shows that any relaxation in regulation would be a retrograde step. Until the industry can prove that it can keep its house in order, then it should be kept on a very short leash indeed.'