Waikato Regional Council is asking the public to be on the lookout for any further signs of aquatic life being impacted on in the region’s waterways.
It follows an extensive investigation which has been unable to determine exactly why hundreds of koura were seen floating down the Oraka Stream in Putaruru shortly before Christmas. No other fish species appeared to have been affected.
The investigation involved taking nearly 50 water samples over five consecutive days, the checking of potential land-based sources of contamination and liaison with the Ministry for Primary Industries (MPI) over possible causes.
“While follow up testing has determined that the aquatic environment in the stream at Putaruru is now a healthy one, we haven’t been able to find the cause of the deaths despite our best efforts and those of other parties,” said investigation and incident response manager Patrick Lynch.
“We’ll remain vigilant for any further reports of aquatic organisms dying like this and ask that the public alert us promptly to any similar issues anywhere so we can follow up promptly.
“For now the stream is supporting all of the fish species that you would expect to see, including koura, trout and eel.
“This appears to have been a short term, isolated incident with no lasting effects on the Oraka Stream or the ecosystem it provides for.”
The council’s chief executive Vaughan Payne praised staff who he said had put in a “huge effort” to track down the cause of the deaths, “including taking samples on Christmas Eve”.
Mr Lynch said one potential cause of the deaths – a disease which affects crayfish - was able to be ruled out by testing of koura bodies by MPI.
The ministry said in a statement to the council that investigations carried out at the animal health laboratory at Wallaceville in Wellington did not find any exotic disease in the koura: “This included crayfish plague, a cause of crayfish mortalities internationally, and which is exotic to New Zealand and listed as an unwanted and notifiable organism.
“The ministry appreciates the support of council in providing the samples for disease testing. Our biosecurity system relies on local authorities, communities and individuals supporting investigations such as this.”