Ireland is neglecting its shellfish stocks by failing to keep clean the waters where they can be found, the European Court of Justice (ECJ) ruled yesterday.
The court also found that the environment authorities had not "designated" enough areas as shellfish waters, breaching an EU environment law from 1979.
The European Commission brought the case before the Luxembourg court on three counts, all of which were upheld in the final judgment.
The court found that the 14 designated shellfish sites were not sufficient; it agreed with the commission that Ireland was breaching EU law by not setting out in numerical terms exactly how much pollution is allowed in the water and it said that Ireland had breached the directive on a third count by not establishing "pollution reduction programmes" for waters that should be designated shellfish waters.
It is now up to the commission to monitor the situation to see if Ireland complies with the ruling.
The judgment comes on the back of a long-running dispute with the commission over how the State is managing its shellfish stocks.
The commission sent a letter of complaint in December 2002, followed by a "reasoned opinion" in 2003 before finally taking the country to court in 2005 after declaring itself dissatisfied with the two responses it had received from the Government.
Irish Shellfish Association (ISA) chief executive Richie Flynn welcomed the ruling, which arose over a complaint it lodged with the European Commission in 2001.
Some 14 bays were designated by the Government under the relevant EU directive in 1994, with no subsequent pollution prevention plans, but some 60 bays have shellfish activity, Mr Flynn pointed out.
"Successive ministers had been ignoring the 1979 directive, as they felt it was too costly to implement, and now we hear that it is going to cost €1 billion to implement adequate pollution prevention measures - as a result of their own stalling.
"It is very good for the environment generally, and for those people living on bays with an oyster or mussel farm.
It will be like having a watchdog, as the Government is now legally obliged to survey the bay, identify all the sources of pollution and take appropriate measures.
"Unfortunately, the worst offenders have been local authorities, through pumping raw sewage and poor planning decisions." The ruling is the latest in a series of judgments and actions this year that have shown up Ireland's poor record on the environment.
In March the European Commission raised the prospect of fines because the Government had ignored two ECJ rulings - one on freeing drinking water supplies of E.coli and a second on introducing tighter controls on discharges to surface water.
The commission added it was taking the country to court for failing to pass legislation giving citizens the right to easily challenge the legality of public authority decisions on environmental grounds.
At the beginning of the year the court ruled the Government was breaking EU conservation law by not protecting the State's natural habitats and wildlife.