A multi million-dollar upgrade of the Ross Creek reservoir in Dunedin is about to begin.

The Dunedin City Council is tendering for the construction work, expected to start in January and take 18 months.

The project budget is listed on the council's website as $6.7m.

It's expected to save the council millions in future expenses to do with the city's water supply.

During the upgrade popular walking tracks around the reserve will be closed to the public.

Signs will be installed warning people of the construction site, which will be fenced off.

Made with the support of NZ on Air