Final rain garden at Isabella Plains in ACT Healthy Waterways project

The $94 million project, part of the Murray-Darling Basin Plan and jointly funded with the Commonwealth, has seen ponds, wetlands and rain gardens built and creeks restored since 2017. Wetlands have been created in Evatt, Holder, Melba, Monash, Fyshwick, Narrabundah and Kingston.

The project was designed to reduce the amount of nutrients, sediment and pollutants entering waterways.

The end of the project was marked by Senator Zed Seselja and ACT Minister for the Environment Mick Gentleman at the rain garden in Isabella Plains, which Mr Gentleman said was the largest in the southern hemisphere.

The work included University of Canberra research into improving water quality in Lake Tuggeranong, which has been plagued this year by blue-green algae, so bad it was described in March by University of Canberra water ecologist Ross Thompson as "almost like a green enamel paint".

Dr Fiona Dyer has led a team of researchers from the University of Canberra to investigate how pollutants behave in local lakes and ponds to improve management.

Once the source of nutrients had been tracked to establish whether a contaminant was involved, "then you can start to say "we need to put in another rain garden here in particular" or "we need to tap a few business owners or land owners on the shoulder and say "what are you doing because it's putting nutrients into the system"."

Senator Seselja said the $85 million federal government investment was vital for the future of the ACT and the Murray-Darling Basin water management.

"This project represented a once in a generation opportunity to significantly improve water quality in the ACT's lakes, as well as the Molonglo and Murrumbidgee rivers and the broader Murray-Darling Basin," Senator Seselja said.

Mr Gentleman said the projects were world leaders in size and scope.

Two hundred volunteers had monitored 232 waterways across the region.