Opuha Water Ltd has published its most recent quarterly water quality report, which focuses on eDNA sampling and biomonitoring undertaken in the Kakahu River earlier this year.
In a statement, Opuha freshwater specialist Dr Jared Panther said finding kōura eDNA was significant because local anecdotal reports had suggested the threatened species was no longer present in the Kakahu.
Dr Panther said it was found upstream and downstream of the Opuha Water Ltd discharge point into the Kakahu River, and upstream and downstream of the gorge.
"Kōura are more active at night and usually seek shelter from predators during the day, which is one reason why they are not easily observed in waterways during daylight hours."
He said eDNA for freshwater mussels, longfin eel, shortfin eel, upland bully, common bully, Canterbury galaxias, torrent fish and brown trout was also detected upstream and downstream of the discharge point.
Opuha Water published its quarterly water quality reports for Lake Opuha and the wider scheme catchment to share the results of the company’s extensive water-quality monitoring programme with the community.
He said the three main ecological aspects of the survey investigated to determine if a measurable impact of the discharge could be discerned were: periphyton (material that grows on the surface of rocks on the bottom of a stream or river which provide habitat and food source for macroinvertebrates), macroinvertebrates and fish.
"The levels of periphyton cover in the Kakahu River in March 2024 remained below guidelines set by the Ministry for the Environment and Environment Canterbury for thick mats and long filamentous algae. There was an increase in periphyton cover at the sampling site immediately downstream of the discharge point, relative to other sites, which could be due to a localised effect of the discharge, but could also be due to other factors such as river works undertaken at the start of the irrigation season. However, there were no patterns evident in periphyton cover at the other downstream sites, which indicates there are no wider impacts of the discharge on the periphyton community."
There were no significant statistical differences in the MCI scores between the site immediately upstream of the Opuha discharge and all downstream sites in the Kakahu River.
"Comparing the 2024 survey with the previous two surveys, there are no consistent patterns in macroinvertebrate community diversity, abundance or quality that would indicate any significant adverse effects of the discharge. Attributing a discharge effect is difficult, as different habitats in the Kakahu River will naturally give rise to different macroinvertebrate scores. High abundance and diversity of fish at sites downstream of the discharge indicate that the discharge is not adversely affecting the fish community."
