A major mould infestation at Athabasca Delta Community School in Fort Chipewyan, Alta., has forced students and teachers to move their classes to an arena for the time being.

The northern Alberta K-12 school has been closed since April 29, after mould was initially found in several classrooms, the library and a hallway.

The school was supposed to re-open on May 4, but more mould was found in the building. Parents decided they did not want to send their children back until the infestation has been completely cleaned up.

"It's frustration on our part. I mean, we have all the kids and, you know, it's like a one-room school," Alice Rigney, a Dene instructor at the school, told CBC News on Wednesday.

"We have what we call our mobile classroom; we're carrying stuff around from table to table."

It is not clear how long the mould has been around, but staff reported noticing an odd smell about a month prior to the school being closed. Rigney said staff also reported getting headaches.

Northland School Division acting superintendent Don Tessier said experts are conducting a full environmental assessment of the school building.

"People are going to come in and look at the furnace. We're going to have other people coming in and looking at the air quality — all aspects of the school," Tessier said.

But Rigney said the best solution to the mould problem would be to move the school altogether, since it was built on a muskeg.

"A lot of the elders actually spoke of it and said that they knew that the school was being built on a muskeg, and that this would happen," she said.

"Sure enough, 25 years later we have mould."

Tessier said investigators with Alberta Ministry of Infrastructure had already determined that the mould was caused by a leak from an upstairs washroom and another leaking pipe in the building.

"As far as the experts are telling me, there's no connection between where that school is located and the development of mould," Tessier said.