Simon Gibb said local groups were disappointed by the lack of consultation on an application to lower the levels of Lake Hāwea despite months of advocacy.
Contact Energy has lodged an application to lower lake levels to 336m for a significant part of the year, 2m lower than the current operating minimum.
The minimum operating level of Lake Hāwea was originally set at 336m above sea level (masl). This level was established during hearings with the National Water and Soil Conservation Authority (NWASCA) in 1980, as part of a broader effort to define statutory lake management parameters.
However, following a 1985 review, and later formalised by the Environment Court in 2007, the minimum operating level was raised to 338masl, with the operating range defined as 338 to 346masl for hydro-electric generation purposes.
Lake operating levels were formalised in a 2007 Environment Court resource consent. That legal framework remains the route to assess the impact of any proposed changes.
The company is permitted to manage the lake between 338 and 346masl, with contingent storage as low as 336masl in the event of a major threat to electricity supply.
The proposed changes would lower the standard operating range minimum to 336masl and the contingent storage minimum to as low as 330masl. Guardians of Lake Hāwea began their advocacy months ago, calling to be more involved in a process they feel impacts the whole community.
Both the Otago Regional Council (ORC) and the Queenstown Lakes District Council (QLDC) have contributed to the application, but this is not available for the public to view.
Guardians of Lake Hāwea chairman Geoff Kernick said although it was not required for the application or council comments to be shared with affected parties, they still felt the community had a right to know.
"It’s mandated that the councils have to respond, but it doesn’t say that the affected parties need to," he said.
"It doesn’t mean we can’t be invited, and we asked to be invited, but we weren’t."
Mr Gibb was concerned about the minimal involvement and presented the group’s opposing views at an ORC public forum this week.
Both groups have been asking the ORC and QLDC to oppose plans by Contact Energy to use fast-track legislation to lower the level.
"There’d be a lot more turbidity in the lake, much more exposed areas, mudflats, shingle fans," Mr Gibb said. "Navigation would become more hazardous."
He said the group had information that showed a 2m drop in lake level could expose up to 20m of additional shoreline in many parts of the lake and as much as 1km at the head of the lake.
This would have significant impacts on fish populations and aquatic ecosystems, as well as greatly restricting access to the lake for fishing and other recreational activities, he said.
The Upper Clutha Angling Club was concerned that any significant drop would also expose submerged plants to frost and weather damage as well as wave erosion, impacting water clarity and key fish nurseries.
Contact has yet to make its case for lowering the operating level of Lake Hāwea.
The government has twice declined to consider the proposal.
Contact Energy was unable to respond by deadline.
