Serious incidents of vandalism have occurred to rock art sites over the past few years. While natural agents of destruction can often be mitigated by protective measures, vandalism is often immediate, catastrophic and irreversible. The West Coast Trail and Mazinaw Lake are two petroglyph sites with vandalism problems. Graffiti may be spray painted or incised over the rock art. At Mazinaw Lake conservators attempted to remove the paint with Super Polystrippa and disguise the scratched areas with graphite pencil and algae-containing mud.