Brush fire burns near Denver Water treatment plant in Roxborough

A brush fire burned near the Denver Water treatment plant in Roxborough on Tuesday evening. Firefighters from West Metro Fire Rescue rushed to the fire just after 5 p.m.
At the time, the fire was estimated to be about two acres and was increasing in size. 
CBS News Colorado’s helicopter flew over the fire which showed charred grass near structures at the treatment plant. 
What caused the fire is being investigated.