"Not only had trout, eels and bullies evidently been killed in the flush, but the thick layer of sludge left in the stream would have killed all the aquatic insects, essentially destroying the entire ecology of the stream," he said.
Teal said it could take years for the Birchville stream to recover.
While he said the regional council took immediate responsibility, he believed it had not learnt from its mistake.
"Despite the ruling today, the sad aspect is GWRC has applied for a resource consent for ongoing maintenance works on the Birchville Dam which could involve more flushing events," he said.
- RNZ