A $385 million irrigation scheme in Canterbury is under fire for unorthodox testing of it's fish barrier.

In Central Plains Water's resource consent, native fish, trout and salmon must be kept out of the irrigation race with a barrier.

Environment Canterbury has discovered the scheme used an unapproved method for testing their barrier, at the end of last year.

ECan advisor Richard Purdon said Central Plains used frozen mixed vegetables.

"We don't endorse the use of frozen vegetables as a proxy for fish. Our response was to note that they didn't comply with the resource consent."

Purdon said that's not up to scratch with the consent.

"We rely on experts in this field such as Fish and Game and DOC to come up with the tests so they can't just go ahead and use, in their case, frozen vegetables."

Salmon Angler's Association member Paul Hodgson said it's not just fishermen that lose out if the barrier's not properly tested.

"The biggest laugh of the whole thing is farmers don't want the fish in the irrigation raceway because it blocks all their irrigation pumps."

Hodgson said it's ludicrous, and will go down in angler's folklore.

The Government's lent $72.5 million to Central Plains Water developments.