On Thursday last week, a member of the public alerted Otago Fish & Game to dead trout in Bullock Creek behind Wānaka residential sections.
Fish & Game officer Mason Court said staff inspected and found six dead trout within a 50m stretch of the creek downstream of Roche St.
The fish appeared to have been dead for one or two days, and there were no visible causes of death, he said.
"While we don’t know exactly what’s happened, it was likely the fish were killed by toxins entering the stream", Mr Court said.
"This looks like a localised water quality issue.
"A longfin eel and juvenile brown trout were found alive in the same stretch of water later that evening, suggesting that whatever had killed the other fish been rapidly diluted by the fast-flowing creek."
Mr Court said the spring-fed creek in the heart of the resort town was important spawning habitat for brown and rainbow trout, and supported native fish.
"It’s a timely lesson of how careful we all need to be to keep contaminants, such as cleaning fluids, paint or chemicals, out of waterways."
Fish & Game collected the fish and contacted Otago Regional Council, which sent an inspector on the same day. They were given to the ORC to be tested.
"Bullock Creek originates in Fish & Game’s QEII-covenanted Wānaka Hatchery Springs wetland, where thousands of hours of community volunteer work has gone in to restoring habitat", Mr Court said.
"But it takes a whole village to look after our waterways."
Before this latest incident, the naturally pristine creek has been flooded with sediment runoff since the expansion of urban development above the wetland.
The Wānaka fish kill follows the discovery of 15 dead trout at Coalpit Dam, near Naseby, on Monday last week.
The cause of both incidents is still under investigation.
— Staff reporter
