With funding from the late Timaru financier Alan Hubbard, the dam has had a chequered history from its inception.
Chris Hutching talks about Timaru water safety on NBR Radio and on demand on MyNBR Radio.
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Arsenic and DDT found in the Opuha River below the Opuha irrigation dam has threatened the water supply of 46,850 Timaru residents.
The river is one source of Timaru’s drinking water supply.
Authorities have stopped using the water from the river and claim the town water supply is completely safe.
Environment Canterbury contractors used a digger to remove sediment containing the poisons on Wednesday afternoon.
It is unclear how long the DDT and arsenic has been there but Environment Canterbury believes it was dumped recently because the chemicals were still in granules.
The inevitable question for police investigating is – who would have access to such chemicals?
The group that originally raised concerns about DDT and arsenic dumping says Environment Canterbury is engaged in a whitewash.
The Opihi Catchment Environment Protection Society says the Opihi River is “dead” when it emerges from the dam, with the inference it is contaminated.
Initially there were problems with the water in Lake Opuha becoming anaerobic from the breakdown of organic matter, requiring belated installation of an aerator.
Another problem has been with the river weed phormidium thriving downstream because of lack of flushing flows.
The irrigators argue the flows have been made more reliable and they cite a 2006 report claiming the dam added $126 million to the southern Canterbury economy.
The dam is about 17km north-east of Fairlie covering up to 710ha when full and storing 74 million cubic metres of water.
Water from the dam is used to irrigate 16,000ha from Fairlie to the coast.
It is often featured as the “poster boy” for Irrigation NZ but it has had a chequered history.
The late Timaru financier Alan Hubbard had a significant role in arranging funding for construction of the dam which began in 1995.
On Waitangi Day 1997 three days of solid rain in the upper catchment resulted in the partially completed dam being overwhelmed by a deluge which wiped out the approach to the Skipton Bridge, ruined vast tracts of farm land, killed stock, and flooded a house at Raincliff Rd.
Damage to the dam was about $8 million with a further $4 million of damage caused to farmland downstream.
The lake was officially opened in November 1998.
During the past summer the lake virtually dried up and Environment Canterbury has allowed the dam operators to reduce outflows and hold back more water to fill the dam in time for this season’s irrigation.
There have been tensions between anglers and the irrigators since the dam was mooted.
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