Work to repair three 250-year-old dams partly damaged by invasive crayfish has begun at an historical beauty spot in Bath.
The restoration at Prior Park will see the dams strengthened, an empty lake refilled, and a cascade reinstated.
The garden will remain open for the duration of the work to enable visitors to see the project first-hand.
The National Trust, which owns the site, previously said the work would cost £2.2m.
The restoration will fall into three phases, with preparation and protection works taking place over the next couple of months.
The main engineering works which includes conserving the stonework of the middle dam, upgrading the lower dam's outlet and re-profiling the banks will be carried out throughout 2020.
The final landscaping phase will see trees and shrubberies planted.
Head gardener Alice Norland said: "Having the contractors on site is a really momentous stage of the project.
"We've been busy readying the garden for their arrival and we've already seen a lot of changes and progress made.
"Reaching the main engineering phase of the project is very exciting."
Simon Dunn of contractors Alun Griffiths Ltd said: 'We look forward to working closely with the garden team to return the historic structures to their former glory."
The National Trust previously said as many as 100,000 American signal crayfish had burrowed into the dams and banks.
It is thought the large and aggressive species - Pacifastacus leniusculus - arrived in the park about 19 years ago from the River Avon, but the problems only emerged in the last decade.