Thousands of homes in the Cowichan Valley will be left in the dark Sunday as BC Hydro performs planned upgrades that will halt power to more than 4,000 customers.

More than 700 customers in North Cowichan and 3,600 in and around Lake Cowichan will be affected by the outage, which could last nearly 12 hours.

About 100 hydro workers are coming to the region to do work between 8 a.m. and 7 p.m., said BC Hydro spokesman Ted Olynyk, who called the outage a “big event.”

It’ll affect areas in Lake Cowichan including Mesachie Lake, Youbou and Honeymoon Bay and its surrounding areas, and in North Cowichan, homes within the boundaries of Limerick Road to Johnston Road and Somenos Road to North Road and Moorfield Road.

Planned work will take place in other South Island municipalities like Langford on Sunday, but is not expected to affect a significant number of customers.

For more information, go to BC Hydro’s outages page here.