Environment Canterbury is investigating the cause of a decline in water quality at the Ahuriri arm of Lake Benmore.
This year's water quality monitoring showed increased nutrient levels in the lake - the trophic level index (TLI) for Lake Benmore's Ahuriri arm increased to an ''unacceptable'' 2.9, a statement from the regional council said.
Last week, the council reported to the Upper Waitaki Water Zone Committee about the action required to address the increased nutrient levels in the lake, including examining nearby irrigation activity.
The increased trophic levels triggered a regulatory process to determine if 10 consent-holders were responsible for exceeding 2.75.
Another five consent-holders, part of the same Ahuriri Arm catchment area, would also be investigated.
A two-person scientist panel of one expert nominated by the regional council and one nominated by the consent-holders would be formed to review the relevant consents.
Last year, the TLI of the Ahuriri arm was within the acceptable range at 2.3.
TLI was not used as an indicator of safety for swimming, ECan said. Land and Water Aotearoa reports the sites monitored in Lake Benmore are generally suitable for swimming, based on three years of summer E. coli monitoring.
The Ahuriri arm of Lake Benmore runs parallel to State Highway 83 between Omarama and Otematata.
