A small fire in a ninth-floor apartment inside the River Place Towers on Thursday evening activated a sprinkler head that helped douse the fire, but which also sent water cascading down through the building to as far as the fourth floor, according to firefighters.

Deputy Chief John Dowling said crews were called to the towering building about 4:30 p.m., and discovered there was a small fire in a bedroom on the ninth floor. The cause of that blaze remains under investigation.

The blaze activated a spinkler head, which sent water flowing from the ninth floor apartment all the way down to the fourth floor, Dowling said.

Firefighters spent about an hour at the scene, with much of that time sent helping residents cover their furniture and other valuables with salvage covers to protect them from water damage.

There were no reported injuries.