The flows - ranging between 600 and more than 800cumecs - have been stripping the invasive algae didymo from the river's main channels.
"When you watch what is coming down under the [State Highway 83] bridge at Kurow, you wonder where it is all coming from," Central South Island Fish and Game Council officer Graeme Hughes said yesterday.
Meridian Energy has been spilling water from Lakes Tekapo and Pukaki through the Waitaki River hydro power generation system since earlier this month, boosting the flow of the lower river well beyond its normal average of about 380cumecs.
Heavy rainfall in the upper catchment filled both lakes, forcing the spilling of water to cope with inflows.
The Waitaki River has been running high and discoloured since January 11, limiting trout fishing to spring-fed or small side braids.
However, Mr Hughes said the flows had been stripping didymo from the main braids of the river, although it was likely to remain in side braids as it did when Meridian released a lot more water - up to 1400cumecs - last May.
He said the removal of didymo from the main braids, which were used by salmon to get upstream, would benefit salmon anglers.
The peak of the salmon catch has been mid to late March in recent years and Mr Hughes said the benefit would exist until then.
"It will be better than if excess water had not been spilled," he said.
Apart from trout-fishing, the other effect on recreation would be jet-boating, with jet-boaters needing to take care to ensure mats of stripped didymo did not block intakes on their boats.
