Amateur photographer Alistair Fraser first noticed the pictograph that hangs above Kootenay Lake was damaged last week.
Blue paint blotches now stain a scene of what appears to be two native hunters.
Fraser says he has a hard time understanding that kind of vandalism.
"They are a part of native culture. They speak to the deep ancestry of us all in many ways."
While police investigate, provincial archaeologist Al Mackie is trying to decide what to do next. He says if the paint splatter is water soluble they'll just leave it and let rain wash away the vandal's handiwork.
"If it's the kind of material that really adheres to rock, then to remove it becomes a pretty complicated process. You need a trained museum person who knows what kind of chemicals to apply."
The pictographs have legal protection and anyone caught willingly damaging them faces a stiff fine and even jail time.