Waterways Ireland, which is responsible for inland navigable waterways, said the findings of a full report into the alleged sewage spillage at Dublin's Grand Canal Dock in Dublin on Thursday could be known as early as Monday.
More than 10,000 fish had to be rescued and many died when oxygen levels in the basin fell to dangerously low levels due to the emergence of "floating solid material" in the water.
The alarm was raised when Dublin City Council workers noticed a potent smell and dead fish floating on the surface. Waterways Ireland and the Central Fisheries Board began a rescue effort.
The lough was opened to allow live fish escape into fresh seawater.