However, rising numbers of brumbies meant there were now about 50 crossings on that section.
«It’s only going to get worse,» Associate Professor Lintermans said, estimating the cost of fencing at $60,000.
The horses stir up fine sediment in the water, which smothers the insects that the fish feed on.
Worse, fewer of the fish’s eggs survive because the sediment either smothers the eggs — preventing them from breathing — or it reduces the ability of the eggs to stick to the underside of rocks to grow so they get washed away instead, he said.
Last year, the Berejiklian government reversed earlier plans to reduce horse numbers in sensitive alpine regions, including Kosciuszko, and instead legislated to protect them.
Pressure to reconsider the heritage status of the horses will be revived when Parliament resumes after this weekend’s election.
Reclaim Kosci, a group calling for a reduction of horse numbers, said on Wednesday it had secured the 10,000 signatures needed to force a debate on repealing the Wild Horse Heritage Act.
“These horses are [also] destroying the habitats of vulnerable native species such as the corroboree frog, the broad-toothed mouse and the Guthega skink,» Linda Groom, a petition co-ordinator, said.
Labor’s environment spokeswoman Penny Sharpe said a Daley government would repeal the act and boost resources to cut horse numbers and repair water catchment damage.
«The impact of horses on Kosciuszko is severe. The horses are pushing threatened native species to extinction,» she said, adding that Labor «supports any urgent measures that look after native wildlife».
The Herald sought comment from NSW Environment Minister Gabrielle Upton and Deputy Premier John Barilaro.
Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.