The Environmental Protection Agency says it is "aware" of concerns about water quality in north Mayo's Carrowmore lake as a result of run-off from the Shell Corrib gas terminal site.
The agency is "keeping a close eye" on the situation, according to its deputy director-general, Pádraic Larkin.
However, monitoring was the responsibility of the local authority, which was satisfied with testing results to date, Dr Larkin said at an EPA function yesterday at NUI Galway.
Mayo county secretary John Condon reiterated yesterday that quality of water in the lake - which serves north Mayo - met testing limits, although he said it would be incorrect to say that the local authority was "happy" with aluminium levels.
Since last July, Shell has been instructed to treat a "large body of water" which built up when it was transferring peat from Bellanaboy to Bord na Móna land at Srahmore.
The water has contained relatively high levels of suspended solids and aluminium, according to the local authority, and arose when the company hit the "dobe" or under-layer of peat during initial peat transfer.
All work at the Bellanaboy site has been suspended since last year as the company awaits the outcome of a safety review of the Corrib gas onshore pipeline. However, it agreed to install a treatment system, run by a British company, Axonics, to prevent any contaminated run- off into the local river and lake.
John Monaghan of the Shell to Sea campaign, who is one of two accredited representatives permitted to visit the site, said that aluminium levels were being breached regularly, according to the local authority's information.
Water was being passed into the drainage system without testing, he claimed, which had been raised repeatedly with the company and the local authority - most recently this week.
When Shell was unable to provide answers to the campaign's concerns on Wednesday, some "very frustrated" local protesters entered the terminal site without accreditation, Mr Monaghan said. "We escorted the group off the site ourselves for health and safety reasons and they were there for all of 10 minutes," he said.
The main sub-contractor, Roadbridge, closed the site early on Wednesday as a result, but Roadbridge and Axonics water-testing personnel were back on site yesterday.
