Transport, quarantine treatment and elevated water temperatures in Lake Pieman at the time thousands of juvenile eels were released earlier this month have been identified as key factors in their deaths.
The Environment Protection Authority (EPA) has been investigating the discovery of thousands of dead juvenile eels (elvers) and a small number of juvenile fish in the Pieman River near Rosebery.
EPA Director Warren Jones said officers representing the EPA received a report about the find on the evening of the 14th of January and samples were taken the following day.
"The Inland Fisheries Service later advised the EPA that around 50 kilograms of elvers collected from the Trevallyn Dam had been transported to and released into Lake Pieman on the 9th of January," Mr Jones said.
"Inland Fisheries said that the eels were out of the water for one hour for quarantine treatment prior to their restocking and that the release included a number of dead elvers and fish that had been caught with the elvers."
"We have also been informed of warm water temperature following the elver release into Lake Pieman.
"This is likely to have reduced oxygen saturation in the surface waters of the lake which, together with the quarantine treatment, are considered significant stress factors for the juvenile eels and therefore likely to be key factors for the deaths," Mr Jones said.
Mr Jones said that water samples collected at the time the find was reported to the EPA do not show any untoward findings.
"The water was tested for a suite of heavy metals. The samples found the results were within the normal range for Lake Pieman."
"Samples of the dead elvers and fish were also collected. However, as both the eels and fish were decomposed at the time they were sampled any analysis undertaken at the labs was limited."
Mr Jones said the investigation was now closed.