A government watchdog has launched investigations into whether two of Scotland's leading wild-fish protection groups have broken charity law by collaborating with the multinational salmon farming industry.

The Office of the Scottish Charity Regulator (OSCR) has responded to complaints from a Highland landowner about the activities of the Wester Ross Fisheries Trust (WRFT) and the Rivers and Fisheries Trusts of Scotland (RAFTS).

Jenny Scobie, the owner of the Rhidorroch estate near Ullapool, alleges that WRFT's links with salmon-farming companies have created a conflict of interest that has compromised its duty to protect wild fish. According to environmentalists, the caged salmon industry has damaged wild populations by spreading lice and disease.

WRFT has two representatives from salmon-farming companies on its board of trustees: Henry Dalgety from the Scottish Salmon Company and Ben Hadfield from Marine Harvest. The trust's chairman, John Mackenzie, also receives a small income from a salmon farm on his Gairloch estate.

In a second complaint, Scobie accused RAFTS of failing to conserve wild fish by taking part in a government project to identify suitable and unsuitable sites for new fish farms. "Fisheries trusts on the west coast of Scotland have been playing fast and loose with the rules for far too long," she said.

The OSCR's investigations suggested that something was seriously wrong, she claimed. The protection of wild fish was not being given the priority it deserved, she argued, and the WRFT had a "cosy relationship" with salmon farming companies.

In the last few weeks, Scobie has received letters from OSCR saying that there was "sufficient cause" to contact WRFT to help inform inquiries. It also promised to "look into" the issue raised about RAFTS.

WRFT's chairman Mackenzie accused Scobie of having an "obsession" and a "bee in her bonnet". She had declined invitations to join the board of trustees and to meet to discuss their differences, he said.

"She's an expert at shouting from the sidelines," he told the Sunday Herald. "She appears to think that any links with the fish farming industry in any form is supping with the devil."

Mackenzie pointed out that the industry was huge and powerful, and was not going to go away.

"We work with them to try to mitigate the dangerous effects that fish farming can produce," he said. "We don't think there is a conflict of interest if the interest is declared."

The trust's work had not been compromised, he argued, and it had objected to proposed fish farms. "The allegation that I am in the pocket of the fish farming industry is ridiculous," he said.

"This is a red herring," he added. "I have no concern whatsoever that OSCR will find anything to criticise at all."

RAFTS chairman Andrew Wallace, confirmed that it had received a notice of complaint from OSCR.

"RAFTS has a longstanding and good working relationship with OSCR and will be very happy to co-operate in any way they see fit to address the issues raised by this complaint," he said.

"We are hopeful that this issue can be speedily resolved and will abide by any conclusions OSCR come to on this matter, as we assume will the person who has raised the complaint. RAFTS will not comment further on the examination of this complaint until the formal process has been concluded."