Alliance's Anna Lo told MLAs it was time to "stop pussyfooting around with half-hearted measures" to protect the sustainability of Strangford Lough, on 23 January 2012.
The environment committee chair explained the importance of the modiolus (horse mussel) reefs in the lough and the possible infraction fines levied the European Commission to protect the mussel beds.
Trawl fishing was banned but the reefs remain much reduced, Ms Lo added.
The committee's motion called on the executive to introduce measures to protect and restore the modiolus habitat in line with the EU's habitats directive.
The Ulster Wildlife Trust had brought a complaint to the commission drawing attention to the plight of the mussels, Ms Lo explained.
Michelle McIlveen of the DUP referred to the importance of Strangford as a breeding ground for common and grey seals, and said the assembly should not underestimate the importance of the mussel beds as a filtration system and as a nursery for other species.
Sinn Fein's Willie Clarke was concerned for the livelihood of the fishing community.
He said they had suffered a great financial loss at the banning of trawling and there had been no compensation.
Mr Clarke said the community accepted that something had to be done to protect the mussels but it had been suggested that both pollution and climate change may have had a role to play.
Danny Kinahan of the UUP warned of the dangers of a major European Commission infraction.
The SDLP's John Dallat said the time for playing politics and juggling with the future of Strangford Lough was long past.
The UUP's Mike Nesbitt said he had examined a report on the horse mussels by Queen's University Belfast and could find no conclusive proof that the problem was caused by any current legal activity.
Environment minister Alex Attwood spoke of the importance of the meeting the following day between representatives of the environment and agriculture departments and European Commission officials.
He said the executive had to be on the right side of the habitats directive.
Mr Attwood explained that in some places the horse mussel reefs had shrunk to the size of a dinner plate.
He informed members that the minimum infraction fine would be £7m with the risk of further fines of £500,000 a day.
The minister said there were currently two total exclusion zones for fishing in the lough, and the environment and agriculture departments had agreed to establish two further zones.
Mr Attwood concluded by calling for a marine bill and the establishment of a marine management organisation.
The motion was passed on an oral vote.