The recent fish kill at Woodburn Reservoir catchment area was most likely linked to faulty equipment used as part of the re-stocking process, according to the Department of Agriculture, Environment and Rural Affairs.
Details were given in a DAERA update to East Antrim UUP MLA Roy Beggs after he had called for an urgent investigation into last month’s incident.
The department told the Assemblyman: “Three of the Woodburn waters were stocked in May and to date fish mortalities have only been found at two of them. Reports indicated that only some fish were dead whilst other fish appeared to be unaffected and that anglers are continuing to catch fish at these sites.
“Brown trout are particularly vulnerable to warm water temperatures as the level of available dissolved oxygen drops, especially during still weather conditions. Lakes can stratify and the top layer of water becomes deoxygenated. This can be sufficient to cause ‘natural’ fish kills.
“Fish that die will generally sink to the bottom of a water and once the decay process set in the body cavity fills with gas and the carcass floats to the surface sometime later. Hence, the delay in seeing some of the fish that died sometime after they were stocked at some of the sites.”
DAERA added that a follow up inspection of the stocking equipment has been carried out and “faulty equipment has been identified”.
“The equipment is undergoing repairs as a matter of urgency. These faults would have reduced the level of oxygen in the transport tanks thereby reducing the condition of any fish being stocked out.
“In addition, stocking procedures have also been reviewed and some changes have been identified which will improve the overall process and thereby reduce the event of reoccurrence.”
Elected representatives and environmental campaigners had expressed concern after dead fish were spotted at the surface of Woodburn Reservoir in May.
At the time, NI Water said it would work with the department and it was considered likely that the deaths were as a result of an oxygen deficiency incurred during transport to the site.