ATHOL - The cause of Sunday's fire, which destroyed a restroom and changing area at the Boulder Beach water park at Silverwood Theme Park, remained under investigation on Monday.

"We don't know how it started yet," said Mark Robitaille, Silverwood spokesman.

Robitaille said it appears the fire, which was reported around 2 p.m., started in the male side of the building, which is in the northeast part of Boulder Beach near the Avalanche Mountain family rides.

Robitaille said a state fire marshal continued the investigation on Monday. He said an estimate of the damage hasn't been determined.

"It destroyed the building," he said.

There were no injuries. Robitaille said one person was transported to Kootenai Health due to smoke inhalation.

The fire shut down the water park portion of the theme park for about two hours. Four attractions near the fire were closed for the rest of Sunday during the investigation, but re-opened Monday.

Robitaille said the building will be rebuilt, but since the water park is only open for one more week, it's not an urgent matter.

"We should have the building open for the 2015 opening," he said.

The amusement park portion of the business was not affected.

An off-duty firefighter assisted Silverwood employees until fire crews from Timberlake and Northern Lakes put out the fire.