Why is someone putting sharp spikes in park ponds?

Mondoreb says: "Sharpened steel spikes, hidden in pits and water, have begun turning up in parks and lakes on two continents."

200807171222.jpgA man wading in the water at the Green Lake Boating Center in Seattle felt a "sharp jab in his foot" Sunday while wading with his family. Pat Boltz reached down and found a metal rod. The rod was sharpened by a machine on the end and it hadn't gotten there by accident. Nor were the other 38 "spikes", 2-3 ft. long, found by Seattle police divers.

Much to the park police's horror, someone had planted 39 metal rods in the bottom of the lake near the center and southern docks of the boating center.

This reminds me of something that happened to me about 10 years ago on a train from Greenwich, CT to NYC. When I sat down in my seat, I felt a sharp sting in my butt. I inspected the plastic upholstery and discovered several small slits had been cut into it. Each slit was hiding an X-Acto knife blade pointing upward.
Spate of Hidden Sharpened Spikes Found in Lake, Parks (Death By 1000 Paper Cuts)