'Climate event' blamed for trout and eel deaths at Lake Tutira in Hawke's Bay
Hawke's Bay Regional Council scientists are investigating an apparent "climate-related event" that has killed large numbers of trout and eels at Lake Tutira, north of Napier.
One estimate is that hundreds of fish have died at the lake, beside State Highway 2 between Napier and Wairoa.
The regional council believes the environmental conditions that caused the deaths have now abated and do not pose a danger to people visiting the lake.
Council scientist Andy Hicks said the deaths were probably related to low levels of dissolved oxygen in the surface water of the lake.
Data collected at Lake Tutira showed dissolved oxygen levels had been "atypically low" over recent days while summer weather had brought high water temperatures.
"At this time of year, the warmer surface usually stays separated from the cooler but low-oxygen bottom water. But there is some evidence of mixing – and this would explain the unusually low oxygen seen in the surface water," he said.
"In combination with the high water temperature, the low oxygen levels observed would certainly be enough to explain some fish kills."
Oxygen levels had "crept up" since Wednesday, meaning more deaths were unlikely, but the council would continue to monitor the situation, Hicks said.
Council environmental officer Ian Lilburn said he was unsure if the count of dead fish and eels would reach into the hundreds, as had been suggested.
He had encountered two to three dozen dead trout and a few eels when he visited the lake on Tuesday.
Despite the oxygen issue affecting fish at the lake, the water quality appeared to be "reasonable" meaning there was no public health issue, Lilburn said.
Just prior to Christmas the council warned the public of a non-toxic algal bloom on the lake.
Lilburn said as an algal bloom died off, it could sap oxygen from the lake, which may have been a factor in the fish deaths.
It was not the first time such conditions had led to fish deaths in the lake, he said.