The Masset branch of the Northern Savings Credit Union was closed for half a day after mould was cleaned out of the basement.
Branch manager Loreena Grosse says problems with the plumbing caused water damage in the summer.
The water was cleaned up, but no one realized it had gotten into the crawl space where Christmas decorations and old carpeting were stored.
When the mould was discovered, Ms Grosse said professional cleaners were called.
They worked over the weekend, but when staff arrived on Tuesday, it was apparent the building needed to be aired out.
Ms Grosse said the problem has been completely taken care of.
"We don't want people to think we have a mouldy building," she said.