About 200 trout and two-dozen eels — tuna — were relocated within the stream and separated by an underwater electric barrier to provide a safe haven for mudfish — kōwaro — on Haldon Pastures Farm.
The solar-powered fish fence was set up in 2021 and is thought to be the first of its type in the southern hemisphere.
Three underwater iron structures send out electric pulses to discourage trout from moving upstream — where they would otherwise prey on the mudfish.
This has increased the upstream habitat size for the mudfish from about 800 metres to 8000 metres.
Mr Grigg said he was impressed by the "outside the box" approach to protecting the mudfish.
"It’s great to be involved in something so innovative and totally different.
The project was a joint effort between Environment Canterbury (ECan), Department of Conservation (Doc), North Canterbury Fish & Game, the landowner and Fonterra. Relocated trout and eel went to the downstream side of the fence.
An electric fishing method was used to capture them and they were then put into buckets, measured, and safely transferred.
About 200 brown trout have been shifted since March.
Canterbury mudfish are the most threatened of New Zealand’s mudfish species.
ECan cultural land management adviser Steve Carrick said low water levels helped improve access for the electric fishing.
"This is the second year that we’ve got together for a week and come out and blitzed it.
"This time, we were able to get to areas that we wouldn’t usually be able to."
"Of course, none of this work would be possible without the landowner’s co-operation.
"John’s willingness to give us access to the property and his support of these preservation initiatives, is invaluable."
DOC biodiversity supervisor Craig Alexander said mudfish numbers had been declining over the years, and the barrier was one way of trying to secure populations in the future.
"The next round of population monitoring is due to be carried out in winter, so it will be interesting to see whether there’s any evidence yet of the barrier’s success."
North Canterbury Fish & Game officer Richard Cosgrove said the electric barrier installation and trout removal helped create a network of native fish sanctuaries with little or no adverse effects on recreational fishery values for anglers.
"Working together helps us identify places like Haldon Pastures Spring Creek and its wetland complex, which has a high native fish conservation value and low recreational trout fishery value."
