Life's a gas in bid to bring fish back to the Clyde

Two giant oxygen cylinders have been moored in the Clyde as part of a 1 million trial, which will pump the gas into the river and improve the quality of the water.

The trial is being carried out by a range of public sector partners on a part of the river that flows past Govan, where oxygen concentrations are known to be low.

River water will be channelled into the oxygenation units where it will be injected with pure oxygen before being released. Raising the oxygen levels of the water is expected to produce a much cleaner aquatic environment and help restore the Clyde as one of Europe's premier salmon rivers.

Other species expected to benefit are sea trout, river and sea lamprey, eels and otters.

The Inner Clyde Oxygenation Project is another step in the rehabilitation of the Clyde, which ranks as one of the world's most polluted waterways. Centuries of heavy industry, while bringing wealth to the city, rendered large stretches of the river effectively uninhabitable.

But although there have been steady improvements in water quality since the 1970s - when heavy industry began to decline and the flow of pollutants began to ease - the revival of the river has been held back by low oxygen levels.

Dr Colin Bean, the policy adviser on fresh water for Scottish Natural Heritage policy said that if successful, the "very innovative" process could have a significant impact on the river's biodiversity.

"The Clyde potentially could become quite a significant salmon river in a Scottish and UK context," he said. "But it's not just about salmon, there's lots of other species that have conservation value that have to pass through the Clyde.

Bean added that despite recent improvements the Clyde still had an "industrial legacy" and that because the course of the river had been affected - effectively straightened and deepened - its potential for complete recovery has been "hampered".

The current project was a good example of where remaining problems were being addressed.

Lowered natural oxygen levels in rivers are damaging to wildlife and at certain times of year - when river levels are low and slow moving - can drop to the point which threatens aquatic life.

In certain sections of the inner Clyde, the effect has been made worse by engineering works over the last 200 years to make the river straighter and deeper to allow for navigation. A deeper river means oxygen-rich water does not penetrate to lower depths. An increase in organic matter also lowers oxygen levels as it rots.

In some cases, this forms an almost impenetrable barrier for fish moving up and downstream.The oxygenation units were put in place, suspended from a barge, earlier this month and are aimed at transforming oxyen levels in a 0.6 mile stretch of the river near the Shieldhall Wastewater Treatment Works.

Kenny Boag, of the Scottish Environment Protection Agency (Sepa), said: "Dissolved oxygen (DO) is critical to the survival of aquatic life and low DO levels threaten aquatic life and negatively impact on other aspects of water quality, such as appearance and odour."

If successful in raising oxygen levels, the project is likely to be repeated in future years.

Kieran Downey, the special projects manager for Scottish Water, said: "The field trial will enable the performances and risks associated with an oxygen injection system to be identified, monitored and better understood. This is all part of the development of our long-term strategy for the Clyde catchment.

"Outputs from the trial will allow the Scottish Government to make an informed decision on how to achieve any future improvements to water quality."

In the 1970s, environment officials recorded zero oxygen levels in the Clyde from Glasgow city to Erskine as a result of the city's industrial heritage. Only when oxygen levels reach 60 per cent do large fish begin to move up river.

In 1983 officials logged the return of small salmon to the Clyde after a 120-year absence. It was not until 2008 that the pollution statistics showed that, for the first time in more than a century, not a single stretch between Glasgow Green and Greenock was classed as "seriously polluted".