This is frightening. A man wading in Green Lake on Sunday evening discovered metal rods buried in the bottom of the lake near the boating center, with sharpened ends pointed up. When Seattle police divers investigated on Monday, they found 39 spikes in all, measuring two to three feet long. “We’re horrified,” says city parks spokeswoman Dewey Potter. “There can’t be any other explanation than malice that we can think of.” The city posted signs around the boating center warning people not to swim in the area.