I just found this video. It may not be everyone's idea of art, but it sure is interesting. I'd like to try it sometime. For me, the soothing sound of the water and the balancing of the rocks would be quite meditative.
There was a news story about this activity. Kent Avery apparently balances rocks in Vancouver's Stanley Park as a frequent activity. I couldn't find a clip of the news article, but did find this post about him on Keep it Surreal.
By coincidence, I also found this video on Youtube. It's also about Kent Avery.