The Opuha dam company will release a significant flow of water in a bid to address some of the concerns around algal and didymo growth.
More than 40 cubic metres per second of water, about four times the average flow of the Opihi River, will be released for several hours on Wednesday.
Opuha Water chief executive Tony McCormick said the company had worked with Environment Canterbury and the National Institute of Water and Atmospheric Research over the past few months to organise the release. He was not sure how long the release would last.
"It could be anywhere from an hour to four hours; it really depends on the dam's capacity. The flows are more than has been in the Opuha section for some time and will change reasonably quickly," he said.
"We want to assess our ability to effectively remove and control the algal growth in this section of the Opihi system. If it is successful, we would definitely try it out again in the future. It won't be enough to make a big dent, but we can only work within our capacity."
Mr McCormick said the company also wanted to carry out the release to help with testing its system before its scheduled upgrades, which include the building of a new spillway expected to cost more than $1.5 million.
"It's a major project for us. We hope to start building in spring, and complete it before the end of the year," he said.
Mr McCormick said the problems surrounding algal growth in the South Canterbury catchments were complex. He had spoken to ECan and local catchment groups, such as the Opihi Catchment Protection Society.
"Everyone wants to work out the best way to manage this," he said.
As of last week, there were still extensive toxic algal growths observed in the Opihi River, while public health warnings were also in place at a popular swimming spot on the Waihao River.
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