Two companies generating electricity on the Waitaki River want their rights to water safeguarded.
Genesis Energy and Meridian Energy want the status of the eight Waitaki power stations' hydro-generation resource consents changed to guarantee they will be renewed when they expire in 2025.
Both companies admit the chance of new consents not being issued is very slim, but the possibility exists under the status they have in the 2006 Waitaki catchment water allocation regional plan.
If new consents were not granted, generation would have to stop, reducing New Zealand's electricity supply by 19%.
An Environment Canterbury panel of three commissioners, chaired by retired Environment Court judge Gordon Whiting, has been hearing submissions in Oamaru and Morven on making changes to the plan.
One was to change the status of the generation consents from a discretionary activity, which meant they could be declined, to a controlled activity, which meant they could not be declined although conditions could be applied.
Yesterday, Genesis presented its case for reducing the status of its consents, but that was opposed by the Mackenzie District Council.
The Mackenzie council's legal counsel, David Caldwell, said the community had genuine concerns that altering the status of the consents would give hydro generation priority over other uses, when other uses were just as important.
The council wanted to have a say on water allocation in the future.
The council's consultant planner, Timothy Ensor, said there was no immediate urgency to provide certainty to hydro-electricity generators and any consideration of the consents' status should be deferred until the plan was reviewed.
For Genesis, resource management adviser Richard Matthews said when consents for the operation of the Tekapo system were renewed, the focus should be on conditions under which the scheme would operate, not whether they should be renewed.
''Any status other than this that requires a resource consent clearly contemplates the consent may be declined ...'' he said.
In this case the system would cease operating.
Genesis renewable energy manager Jarrod Bowler said the company made
''the very significant $821million'' purchase of the Tekapo scheme in 2011.
It was essential resource consents for the Waitaki system continued beyond 2025, when they expired, so the Waitaki system continued to provide ''nationally significant generation''.
New Zealand's longest-serving Fish and Game officer, Graeme Hughes, said the Waitaki River was the most fished in the region, and was unique in that salmon, brown trout and rainbow trout could be caught in one outing.
Now retired, he was giving evidence for the Lower Waitaki River Management Society, which opposes changes to the original plan, particularly lowering its 150cumecs minimum flow and the status of generation consents.
Reducing the minimum flow by up to 60% would have an adverse effect on the fishery and wildlife.
''It is a high risk and, once adopted, will be irreversible,'' Mr Hughes said.
Retired teacher John Anderson, also a member of the society, said changing a ''well-thrashed plan'' was ''not a good look''.
''This must be embarrassing for all involved. The plan is due for review in 2016, so there will be another look at the whole thing.''
He supported retaining the present plan and said many people had a strong emotional response to lower flows, and had ''visions of the lower Waitaki being reduced to a stormwater drain''.
