Three cows died and six swam to safety, helped by boats.
Farmer Nick Mead said the mountain bikers had ignored signs saying the road was closed and stock was coming out.
Mead said when she caught up with the bikers, they told her they thought the road closure only applied to vehicles.
It is believed the bikers were from Whangārei.
After the accident, Mountain Bike New Zealand president Chris Arbuckle and Upper Clutha Tracks Trust chairman John Hare spoke out in support of the Mead family and reminded recreationalists of the outdoors code of self-responsibility and respect for the rules.
The Walking Access Commission is responsible for publishing the Outdoor Access Code of Behaviour, which describes how people should behave when walking and biking, especially on private land.
"We try to find a solution that works for all parties access that works for both the landholder and the outdoor recreationalist.
"A consensus is more enduring than imposing an outcome.
"We have not worked with individual mountain bikers but we do support landowners to develop clear signage and information," Day said.
If bikers were not sure of their access rights, they should call or send an email, they said.
"The best thing bikers and walkers can do before accessing private land is ask first. Explain what they want to do and when. And, in circumstances like this, where access is over a working farm, people need to be clear about the conditions of access on that land, so they do not adversely affect the farm.
"Play it safe and take the cautious approach if you're not sure," Day said.
The commission also offers landowners free signs to mark access routes.
