Two rare native fish facing extinction may not survive in the lower Waitaki and Hakataramea catchments with low river flows, the Department of Conservation warned yesterday.
The lowland longjaw galaxias is New Zealand's most threatened fish, ranked as "nationally critical".
It and the "nationally endangered" Canterbury mudfish have populations in both catchments.
But the department is worried by applicants wanting to take water within the two catchments and have a minimum flow of 100 cumecs in the lower Waitaki River, instead of the 150 cumecs environmental minimum low set in the Waitaki catchment water allocation regional plan.
It is also concerned about minimum flows suggested for the Hakataramea catchment and tributaries of the lower Waitaki River.
Yesterday, it made those concerns known, not just for fish but also for birds, to an Environment Canterbury hearings panel.
Freshwater ranger Peter Ravenscroft said dropping the minimum flow would affect shallow areas, groundwater and wetlands, upon which the lowland longjaw and mudfish depended for survival.
"Given their high risk of extinction, any loss in their respective habitats will be significant and pose a serious risk to the ongoing survival of these species," he said.
The mudfish were on the south bank of the Waitaki River at four distinct locations, occupying wetlands and springs linked to the Waitaki River.
Reducing the river's minimum flow would shrink or remove wetlands, threatening their long-term survival.
Other indigenous fish, including longfin eel, lamprey and torrentfish, were migratory and were at risk from reduced flows in the lower Waitaki, Hakataramea and Maerewhenua Rivers.
There were seven known populations of the lowland longjaw in the Waitaki catchment and two in the Hakataramea catchment.
The Hakataramea population made up half of the known numbers.
Water takes in the Hakataramea had the potential to have an adverse effect on their survival, he said.
Legal counsel Philippa Rutledge said the department wanted to ensure Waitaki and Hakataramea catchment flows and levels continued to support the habitats of braided river birds and indigenous fish, particularly threatened species.
It was also concerned about the implications for the integrity of the water allocation regional plan and its environmental minimum flow of 150 cumecs, which the department supported.
