The term ''flatlining'' was used on Tuesday in an Environment Court appeal hearing in Cromwell to describe the state of the Lindis River and several other Otago waterways at times resulting from the overallocation of water for irrigation.

Niall Watson, on behalf of the Otago Fish and Game Council, was giving evidence supporting a 900 litres per second minimum flow in the Lindis.

He defined flatlining as ''artificially depressed flows for long periods'' and applied it not only to the Lindis but to the Lower Manuherikia and Arrow Rivers, which had ''unnaturally low'' flows, and the Kye Burn, Sow Burn, Pig Burn, Ida Burn, Cardrona River, Quartz Creek, Benger Burn, Low Burn and Bannock Burn, which, like the Lindis, dried up completely during summer.

''Artificially depressed flows for long periods - known as flatlining - remove natural variability, meaning aquatic life does not get relief from stressful low flow events.

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In effect these rivers are subjected to severe artificial droughts every single year.''

This, he said, led to trout and native fish becoming stranded and vulnerable to predation.

The Lindis Catchment Group (LGC) and the Otago Regional Council (ORC) are appealing an ORC decision setting a 900 litres per second minimum flow in the Lindis, arguing instead for a 550 litres per second minimum flow, alongside a move away from using historic water races to bores, known as the ''gallery'' scenario.

Watson supported the gallery scenario but with a 900 litres per second minimum flow.

Farm consultant Grant Porter. Photo / ODT File
Farm consultant Grant Porter. Photo / ODT File

During cross-examination of Watson, LGC lawyer Phil Page pointed out a previous witness, farm consultant Grant Porter, told the hearing this would be uneconomic.

Porter said a 900 litres per second minimum flow with existing water races would make farming ''financially unsustainable in an average year'' and ''even less sustainable'' with the gallery scenario ''because of the additional capital and operational costs''.

Questioned by Alastair Logan for the ORC, Watson said he had heard, ''but didn't necessarily accept'', the galleries would not go ahead if the court set the minimum flow at 900 litres per second.

He understood the water races were ''near obsolete'' and the galleries were ''sort of inevitable''.

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''It seems to me with an ageing race system which is increasingly unreliable, [irrigators] will have to do something in the long term.''

-A witness at Monday's hearing, Suze Keith, appeared in a personal capacity, not as climate change adviser to the Wellington Regional Council.