Swords is the dirtiest of 30 Irish towns in the latest survey published by Irish Business Against Litter, (IBAL).
The north Dublin town edged out Sligo, Maynooth, and Dublin city itself - all named "litter blackspots" - for the dubious distinction.
An Taisce, which carried out the survey for IBAL, said there had been a "huge drop" in standards in Swords since the last league results in August.
The town's "whole attitude to litter and environmental issues needs to change", the judges concluded.
At the the other end of the table, Cavan - the reigning champion - joins Monaghan, Carlow, Fermoy and Wexford on a short-list for the title of cleanest town. The winner will be announced today.
These are among 11 places judged "clean to European norms", the highest number in this category since the league was established in 2002.
Overall, the latest results confirm that the Republic is getting "cleaner and cleaner", according to the business anti-litter campaign with towns averaging 73 marks out of 100, compared with 55 in the first survey.
Even Dublin, which again fared badly, was found to have 15 per cent less litter than last year. "Another 15 per cent and Dublin could bury its 'dirty old town' image," IBAL said.
Moore Street traders - "responsible for an awful situation" according to An Taisce - were among those singled out for blame.
O'Connell Street and Talbot Street were also judged eye-sores, because road and footpath works there had become "litter traps".
Cork, which was bottom of the league last time out, improved to "moderately littered" in the latest survey. By contrast, Galway suffered a "very disappointing" drop in standards to join Dundalk, Navan, Newbridge, and Limerick in the "serious litter problem" category.
An Taisce commented that Galway Docklands Area was one of two litter black spots - it was in a dreadful state. There was one premises, Donnelly's Coal, which was almost solely responsible for the overall grading. The Canal Board Walk was surveyed in two areas, one of which was heavily littered and the other a litter black spot.
Newbridge was the only town in the survey not to have a single site rated "clean to European norms".
IBAL said the overall improvement in standards coincided with an increase in enforcement, with more than 11,000 on-the-spot fines issued by local authorities in the first half of this year, up 9 per cent on the previous six month period.
IBAL chairman Dr Tom Cavanagh welcomed the trend: "Enforcement levels are still too low to be a deterrent, but they do indicate local authorities are finally taking the matter seriously. Business and tourism will no longer accept litter in our high-cost economy, and neither will the population in general."
