Work is underway on the city reaches of Christchurch's Avon River in what is possibly the largest urban river restoration undertaken in New Zealand.
The $96 million Avon River Precinct extends more than three kilometres and is one of the Government's re-build projects for the earthquake-hit city.
Diggers will remove more than 100 years' worth of sediment build-up that the precinct's lead ecologist, Shelley McMurtrie, says is choking the waterway.
Sediment will be washed off gravel in the river and storm water from roads will be filtered through rain gardens before it enters the Avon.
The project includes creating overhangs using rocks to provide habitats for fish, while the banks will be landscaped and planted to support bird life.
Mr McMurtrie says urban waterway enhancement is a reasonably new science, so the project will test new theories on ways to help the river clean and look after itself.
The first stage of the restoration began last year. The project is due to be completed by mid-2015.