Scottish Water has been branded as one of Scotland's biggest polluters after government figures revealed that it has been guilty of 51 pollution offences in the last ten years.

The public water company has been fined more than £240,000 for 47 spills, leaks and discharges between 2005 and 2014. It has been formally admonished by courts for four further incidents.

Recent offences include chlorine discharges that killed over 1,000 young trout and salmon in the Alva Burn near Alloa, sewage contamination of the River Kelvin in Kirkintilloch, and leaks of over 10,000 litres of lethal sulphuric acid into the River Devon in Clackmannanshire.

The average fine paid by Scottish Water over the ten years was £4,700, with fines for 28 of the pollution breaches below that. The company, which is owned by the Scottish Government, turns over £1 billion a year.

The relatively low level of the fines has prompted concerns that they are failing to deter Scottish Water from making blunders that annihilate wildlife. One environmental group is now calling for the company's senior managers to be made personally liable for pollution.

Andrew Graham-Stewart, director of the anglers' organisation, Salmon and Trout Association (Scotland), said that Scottish Water's relentless pollution offences did not inspire confidence. "The organisation's record over the last ten years amounts to a depressing catalogue of failures to curtail breaches," he told the Sunday Herald.

"For a public utility, fines are of little, if any, consequence. We fear that an improvement is unlikely unless the regulatory regime is altered so that Scottish Water's senior managers and directors are held personally responsible and liable."

Dr Richard Dixon, director of Friends of the Earth Scotland, argued that the fines were failing to concentrate the minds of senior executives on cleaning up their act. "It is deeply disappointing that one of Scotland's biggest polluters is a body owned by the people of Scotland," he said.

"It is ironic that water charge payers are funding Scottish Water's fines. More public investment in the infrastructure is needed and could avoid public money going round in pointless circles."

A list of the 51 punishments for pollution offences imposed on Scottish Water between 2005 and 2014 was provided by the Cabinet Secretary for Infrastructure, Investment and Cities, Keith Brown MSP, in answer to a parliamentary question by his Labour shadow, Mary Fee MSP (see table below).

Fee demanded that Brown "come clean" on the problem. "His government's oversight of Scottish Water has led to spiraling pollution and rocketing fines - at the taxpayers' expense," she said.

"The Scottish Government must come before parliament and outline a solution. Keith Brown has been served notice of his government's failure at Scottish Water. He must act - the people of Scotland won't swallow any excuses."

Scottish Water, however, argued that it had reduced the number of "non-compliant" sewage works by 90 per cent over the last ten years, and had seen a 23 per cent drop in pollution incidents in the last year. It had invested more than £1 billion since 2002 to deliver "substantial improvements" to Scotland's environment.

"As a consequence we are no longer the principal pressure on Scotland's water environment," said Scottish Water's chief operating officer, Peter Farrer. "We remain committed to supporting Scotland's water quality objectives, with a minimum investment of £490 million to protect and enhance the environment."

He suggested that it was difficult to compare the company's pollution with that from others, as it had more environmental permits. "We maintain a significant network, including more than 2,000 treatment works and over 60,000 miles of water pipes and sewers," Farrer pointed out.

"Where a pollution incident has occurred we work closely with the Scottish Environment Protection Agency (Sepa) and other stakeholders to investigate, resolve and clean up any watercourse affected, while we have robust emergency procedures to ensure the safety of the public and protection of the environment."

The Scottish Government agreed that Scottish Water's compliance with pollution rules had "significantly improved" in the last ten years. "Any pollution incident is taken extremely seriously and thoroughly investigated," said a government spokeswoman.

Sepa stressed that Scottish Water had to keep improving its performance. "When significant pollution events occur, we may present a case to the Procurator Fiscal for consideration," said Sepa's area manager, Colin Anderson. "We can also employ other forms of enforcement action where necessary to ensure that remedial work takes place."