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The accident happened last week on a notorious stretch of Dingle Burn Station Rd while station farmers Nick Mead and Tim Lambeth were mustering a herd of 60 pregnant cows.
Nine cows plummeted off the remote Dingle Burn Bluff.
Six swam to safety, helped by people in boats.
Two of the survivors swam for several kilometres before they could be rescued.
She said the riders had ignored signs placed before the muster near a Department of Conservation car park, which warned "Road closed! Stock coming out".
Her family had lost faith in the public and would resort to having a person manage the road every time they moved stock in future.
‘That’s the price we have to pay for brainless idiots," Ms Mead said.
Upper Clutha Tracks Trust chairman John Hare, of Wanaka, said the Meads’ distress was understandable.
"I am terribly sorry this has happened. There’s no accounting for what some idiots will do," he said.
Mountain Bike New Zealand president Chris Arbuckle, of Wanaka, said the incident highlighted the riders’ lack of awareness about the environment and their own safety.
"I agree entirely with the land owner.
"The mountain bikers should have turned back.
"It’s about personal responsibility. And common sense," he said.
Ms Mead said the mountain bikers also spooked themselves.
"They saw the mob and got off their bikes and climbed up the bluff to get out of the way."
When the mountain bikers were confronted, they said they thought the road was only closed for vehicles, she said.
Ms Mead said her family now regrets agreeing to public biking and walking access along the road during tenure review.
The access agreement means motorists cannot use that part of road without permission and motorists were also disregarding "no vehicle access" signs, she said.
"... we wish we had never done it. We’ve been so tolerant, but people using rural areas like this need to get themselves properly educated in rural etiquette," Ms Mead said.
Mr Lambeth confirmed recreational access could not be legally revoked.
The criticism did not include the annual Contact Epic Round Lake Hawea mountain bike race.
Mr Hare said the trust’s attitude was that the public must get consent from property owners, treat access as a privilege and accept farming operations could temporarily prevent access.
Mr Arbuckle said all mountain bikers should be familiar with the national body’s code for respect for others, the rules and tracks.