Virginia Lake is clear of the algal bloom that has been affecting the lake since mid-December.
And the all-clear signs around the lake reminding people to wash their hands if they come into contact with the water have been removed.
Councillor Ray Stevens, chairman of the Wanganui District Council's infrastructureand property committee, said lakes across the country had been affected by blue-green algae this summer.
"Virginia Lake was no exception but our algal bloom started much later than in most parts of the country and has now cleared," Mr Stevens said.
"We attribute this to the measures we have put in place to control the development of algae at Virginia Lake, in particular the ultrasound units.
"Unfortunately algal blooms are a natural phenomenon and we cannot prevent them from happening but it's great to know we are able to limit the impact," he said.
Ultrasound at high amplitudes breaks down the cell walls of the blue-green algae, releasing the toxins into the water and dispersing it.
