Scottish Water was prosecuted for pumping sewage into the loch
Scottish Water has been ordered to apologise to an Argyll town after a watchdog criticised its handling of problems at a water treatment plant.
Campbeltown had been plagued with sewage problems since a new water treatment system was installed in 2001.
But Waterwatch Scotland said Scottish Water rubbished residents who complained, and had sought to mislead the public over problems at the plant.
Scottish Water said they were "disappointed" with the report.
Speaking to BBC Radio Scotland, Geoff Aitkenhead of Scottish Water acknowledged there had been problems, but insisted they were firmly in the past: "I think the key message is that we are moving forward with investment proposals and indeed with work on the ground.
"We've spent £3.5m in Campbeltown since the middle of 2008 to address some of the problems.
"We have investment proposals which will see a total of £24m spent in the town to finally address all of the issues."
The utility firm pled guilty last year after being prosecuted for failing to comply with an enforcement notice in relation to the discharge of untreated sewage to Campbeltown Loch from its Kinloch Park pumping station.
The prosecution was the culmination of a long-running series of flooding and sewage problems in the town that had a detrimental impact on several local businesses.
In a damning verdict following the longest inquiry it has ever undertaken, Waterwatch Scotland - an independent body that investigates complaints into water and sewage providers - demanded that Scottish Water issue a "full and unequivocal apology" for its failure to deal with problems at the water treatment works.
It also described the number and duration of sewage flooding incidents Campbeltown has had to endure as "unacceptable".
Waterwatch Scotland convener Heather Brash said the problems for local people caused by sewage flooding were repeatedly compounded by public bodies not dealing with their complaints properly.
"This is a saga of poor planning compounded by the failure of anyone to take responsibility, which has meant huge amounts of money have been spent without providing the community with what it needs," she said.
"Local consumers have never been taken seriously by Scottish Water which tried to discredit the concerns of those who complained and sought to mislead the public.
"From the day an untried system which wasn't up to the job was chosen for Campbeltown nearly a decade ago, pretty well everything that has been done has made things worse rather than better - including adding new catchment areas to the waste water going into the already-failing treatment works."
She said it was only in recent months, when the chief executives of both Scottish Water and the Scottish Environment Protection Agency became directly involved, that a more "robust approach" was taken to the problems at Campbeltown.
A spokesman for Scottish Water said it was "making good progress" in its work to improve the sewerage system in Campbeltown, which remained one of its top priorities.
He added: "We will study the contents of the Waterwatch Scotland report in more detail, and may comment further, but our initial response is that the report is largely about historical issues in Campbeltown and does not accurately reflect the recent work we have done and the progress we are continuing to make towards resolving the problems.
"We fully acknowledge that our work in Campbeltown has been challenging for various reasons but we are disappointed with the Waterwatch report and believe it contains factual inaccuracies.
The spokesman said Scottish Water acknowledged it had not yet achieved the level of service customers should be receiving, but insisted it was "absolutely committed" to making further progress towards delivering a long-term solution, which would put the utility firm back into compliance with its regulatory discharge consent by September.
He added: "We have apologised to our customers for delays in some of the work. But, by its very nature, this has been a protracted process and has involved various agencies including Argyll and Bute Council, the Scottish Environment Protection Agency, and the Scottish Government."
Local Councillor John Semple said the situation had taken a "significant turn for the better" in the last six months after pressure was put on Scottish Water by the Scottish Government.
Mr Semple said he was "hopeful and confident" that the problems would be completely resolved within the next year.