Lime spill kills life in stream

By Margot-Jane Smith

A toxic spill from Dunedin's Mount Grand water treatment station has killed all aquatic life in the Kaikorai Stream for about 10km. About two tonnes of lime was accidentally discharged from a storage area at the Dunedin City Council plant into a tributary of the stream on Wednesday night.

As well as almost 1000 trout, the spill killed eels, crayfish, insects, algae and even worms on the stream's banks. "It's not a minor spill, it's a major, major spill," Fish and Game officer Monty Wright said. "I've worked on fish kills in other places and they generally take out [kill aquatic life for] around 1km. This has taken out kilometres and kilometres of water, so it's a disaster."

There was no risk to humans, he said. It would take two or three years for the stream to return to normal. Dunedin City Council water manager Nigel Harwood said plant staff were unaware of the spill until contacted by the Otago Regional Council. "Once the ORC said `Is there anything that might have affected the stream' people went out and checked everything and said `Hell, looks like it happened here'," Mr Harwood said.

A formal investigation into the accident would be held this morning. However, initial thoughts were that a slurry, including 25% lime, had been put into a storage area with an open valve, which discharged into the creek. Mr Harwood said it was not easy to tell whether the valve was open or not. "It appears at this stage to be one of those human errors," he said. Water was diverted from the treatment plant to help flush any residual lime out of the stream.

Lime was used at the plant to help improve the taste and reduce the corrosive nature of treated water. Mr Wright said the deaths occurred because lime removed oxygen from water.
Some trout and eels had tried to leap out of the poisoned water, and worms had crawled out of the soil and up the bank.

The lime was diluted as it travelled downstream until bigger fish could survive.
"The last dead fish we saw was at Harroway mill [at Green Island] and the first live one was at the Green Island rugby grounds," Mr Wright said. Ducks appeared to have been unaffected.


Friday 27 October 2000

This information obtained from and with the permission of the Otago Daily Times.