Record high water temperatures and low river levels likely contributed to the deaths of more than 80 fish in two South Taranaki waterways earlier this year, says Taranaki Regional Council.
River levels were also particularly low for the months of December and January in the Waingongoro River.
A report to the Council’s Operations and Regulatory Committee revealed 27 fish died in the Waingongoro River and a further 55 fish were found dead in the Kaūpokonui River in January.
An investigation was launched after members of the public alerted Taranaki Fish and Game to the deaths. The affected species included tuna (long-fin eel) and trout.
The investigation revealed that water temperatures in both the rivers were the highest on record and were elevated for several days around the time the dead fish were discovered. Temperatures were up to 5°C warmer than usual for the time of year.
River levels were also particularly low for the months of December and January while oxygen levels in the water were extremely high, reaching levels that are toxic to fish. The investigation found no evidence of a pollution incident.
Abby Matthews, the Council’s Director for Environmental Quality, says it was difficult to identify any single cause of the fish deaths.
“It’s likely that the combination of high temperatures, low flows and oxygen toxicity all contributed to these events. We’d like to thank the public who brought this to our attention so we could respond quickly. It’s important we investigate issues such as this and try to find the cause.
“Unfortunately these types of environmental extremes are likely to become more common with the effects of climate change.”
Ms Matthews added that the total number of fish deaths is likely to be higher than the number reported given that some could have been scavenged or washed out to sea prior to the investigation.
The Council is currently seeking views on freshwater targets for the region’s rivers and streams. To have your say, head to www.trc.govt.nz/helpshapetherules(external link) to see information on targets for E. coli, nutrients and sediment and targets and limits for water take and take part in surveys.
To report pollution or incidents involving Taranaki waterways, please call the Council on 0800 736 222 or email info@trc.govt.nz.