Northumbrian Water is set to invest £6.9m in Selset Reservoir.
The work will add long-term resilience to the site’s ability to support water treatment for customers in Teesdale and beyond.
A spokesman for the utility company said: “Earlier this year, work was carried out by our partners, Esh-Stantec, to establish elements of the site, ready for work to start in earnest following the nesting season, for up to 18 months.
“While some elements of work will take place during the nesting season, these will involve minor activity, sensitively managed to ensure no disturbance.
“We are already in contact with the site’s neighbours, to let them know what to expect, and will be keeping them informed of progress and any activities that may impact them.”
The work will include renewing the site’s pipework and related infrastructure, and enhancing management of flows that are passed forward for treatment at Lartington Water Treatment Works.
The spokesman added: “During the course of the work, we will have a compound established on the main car park, and visitors will be directed to alternative parking on site.
“Access across the dam will remain open for most of the work, although there may be times when temporary closures are required.”
