Samples of small animals that lack a backbone and live underwater are to be collected and analysed on the Blackwater River at Mallow in Co Cork, as the authorities continue their quest to find the cause of the devastating fish kill in the area two weeks ago.
These macroinvertebrates that are now part of the investigation include bugs, mites, crustaceans, leeches, worms and aquatic snails.
The authorities are hoping that sampling these creatures might help them locate where along the banks of the Blackwater the environmental irritant that caused the massive fish kill entered the water.
Precisely what the environmental irritant was, however, is still unknown.
The results of the detailed analysis, including toxicology of the dead fish by the Marine Institute, are expected to be completed over the next week.
Preliminary results delivered last week by the Marine Institute found that the fish kill was not caused by bacterial disease, fungal infection, low water levels or high temperature in the water.
That report said instead that a significant yet so far unidentified "environmental insult" had caused what local anglers claim is the largest fish kill in the history of the State.
The EPA sampled and investigated outflows from all EPA-licensed businesses and industrial operations in the area at the time of the fish kill.
Their results suggested the water had not been polluted by any toxic outflow from the entities they license.
Inland Fisheries Ireland estimated between 8,000 and 10,000 fish were killed along an 18km stretch of the river.
However, local Anglers who entered the waters themselves and collected a sample of 3,500 dead fish in a small stretch of the river estimated that over 40,000 fish died in a 30km stretch of water.
Since then, the anglers have said they believe as much as 50km of the river may have been affected, and so the number of fish killed could be even higher.
Last Friday, a meeting took place in Mallow between the anglers and the stakeholders involved, including the Minister of State for Fisheries and the Marine, Timmy Dooley, Inland Fisheries Ireland, Cork County Council, the Environmental Protection Agency, the Marine Institute, and Uisce Éireann.
Following that meeting, Minister Dooley called for enhanced collaboration among the state agencies to find a cause for the fish mortalities.
In a statement today, Inland Fisheries Ireland, which is coordinating the interagency group, confirmed that all the agencies are working closely and have been discussing potential actions to progress the investigation.
It said the potential actions include testing riverbed sediment, analysis of fish mortalities for harmful substances, and sampling aquatic insects, bugs and molluscs - which it referred to as macroinvertebrates.
It also said Cork County Council, the EPA and IFI will extend their work this week to further assess water and habitat quality overall.
IFI said it will continue to inspect the affected channel of the river and its tributaries for dead or affected fish and will be liaising closely with all State bodies on the matter.
Agencies are also reviewing historical data to see if any reports received in recent months may be relevant to the incident.
