Barwon Water has applied to the Environment Protection Authority (EPA) for permission to conduct an emergency release of recycled water into Port Phillip Bay at Portarlington.
Demand from recycled water customers has fallen dramatically due to above average rainfall over the past 12 months, leaving recycled water holding lagoons at the Portarlington water reclamation plant at capacity.
The high rainfall has produced inflows to the plant four times higher than average and, with the possibility of further winter and spring rainfall, Barwon Water needs to make room in the storages.
Barwon Water General Manager Water Systems Carl Bicknell said releasing excess water to the bay was the best alternative after all other viable options had been exhausted.
"The near-saturated soil means that release to nearby Barwon Water land is not possible and transporting the excess recycled water by road to the Geelong sewerage system would require an exceptionally high number of heavy vehicle movements from the plant," Mr Bicknell said.
"We estimate 10 to 15 semi-trailers would need to operate around-the-clock for three months to transfer the excess recycled water - a total of more than 7,100 trips."
Barwon Water estimates up to 200 million litres of Class C recycled water will be released into Port Phillip Bay via a stormwater drain over the coming months.
A number of agencies and community groups have been consulted.
Mr Bicknell said an independent aquatic ecology specialist had conducted surveys at the potential release point and a rigorous ongoing monitoring program would be implemented.
"The clear water is classified Class C recycled water under EPA guidelines and is suitable for irrigating public open space, certain crops and sporting fields, including golf courses," he said.
Barwon Water received permission from the EPA last year to conduct an emergency release from the Bannockburn water reclamation plant to Bruce's Creek when the recycled water lagoons reached capacity.
An independent review at that time found there was "no detectable impact on water quality" in Bruce's Creek or further downstream in the Barwon River during the release.
A major upgrade of the Bannockburn plant, including new winter storage lagoons, is currently underway.
Mr Bicknell said the corporation was investigating options to prevent possible future emergency releases from the Portarlington plant, including connection to the Geelong sewerage system.