NCA boss Gary Rake said data from the first year of the trial into water quality returned a mixed response, with little variability found between trial and control sites. But he said the results were positive enough to continue the probe for the remaining two years.

Two solar-powered water circulators - costing $85,000 each - were installed at Molonglo Reach and near the swimming beach at Yarralumla Bay in September last year.

Water quality near the circulators was tested each week and compared to control sites.

Mr Rake said results showed the water circulators had the most impact during the warmer summer months when stratification increased.

The circulators work by mixing cold, acidic water from the lake depths with warmer water on the surface.

The motion helps prevent the release of nutrients, which the blue-green algae feed on.

Mr Rake said the nutrients, much of which entered the lake via the Molonglo River, were in a bound form, which blue-green algae could not readily access. But the nutrients become unbound when they hit stratified water.

The water circulators interrupted the stratification of the water in the lake, so the nutrient remained bound and unable to feed algae blooms.

Mr Rake said the NCA was still uncovering the lake's secrets. He said the type of data collected would be expanded in the coming years, to include wind direction and rainfall, different sample depths and increase regularity of testing.

He said no negative impacts had emerged, with concerns the machines would stir up sediment, affect wildlife or cause a navigation hazard proving unfounded. ''They're doing no harm, possibly doing some benefit and showing enough positive signs to continue with the trial.''