Mystery of Green Lake's metal spikes solved?

When a wading man found metal spikes in the Green Lake muck last week, Seattle parks officials were horrified and said there couldn't be "any other explanation than malice."

"It's so bizarre," parks spokeswoman Dewey Potter said at the time. "We can't imagine who did it or why."

How about the city itself?

Turns out, the dozens of spikes plucked from the lake bottom probably were put there not out of malice but with the best of intentions as part of a campaign launched more than two decades ago to rid the lake of milfoil, a pesky weed that clogs the lake.

Kathy Whitman, city aquatics director, confirmed Friday that looped metal spikes were used in the early stages of milfoil control in the 1980s to hold down plastic sheeting, and the spikes found this month may be those devices. The metal spikes were replaced later with plastic ones, she said.

Friday, volunteer divers from Virginia Mason Medical Center in Seattle searched the south end of the lake and found 41 more metal spikes off the docks at the small-craft center. In all, about 80 of the 2- to 3-foot-long spikes have been found, some with a U-shaped bend at the end.

On Friday, divers also began to speculate that the spikes had been used for weed control. One of the divers, Claude Wreford-Brown with the Center for Hyperbaric Medicine at Virginia Mason Medical Center, said divers found plastic sheeting on the lake bottom and figured the spikes were there to hold down the plastic.

According to a story in The Seattle Times in 1984, the city placed 120,000 square feet of black plastic on the lake bottom near the small-craft center and along the southeast shoreline — where the spikes have turned up.

The idea was to deprive the weeds of sunlight to inhibit their growth, the article said. Then-mayor Charles Royer held a news conference at the lake to explain the scheme.

Still, the spikes remain puzzling to some.

Jason Frisk, of the small-craft center, noted that the area was searched in 2005 and no spikes were found.

"What gets me is, three years ago we pulled out two truckloads of garbage and there was not one rod in it," said Frisk. "Now, they seem to be crawling out of the ground. I don't have an answer."

For now, though, the Seattle police still consider the case open. Sgt. Sean Whitcomb said Friday that detectives are investigating, in case the spikes were placed there with intent to harm. Crime Stoppers of Puget Sound is still offering a $1,000 reward.

"Right now, this is a criminal investigation," Whitcomb said. "If we receive any information to the contrary, we'll revisit that."

Meanwhile, the parks department said Friday it is going to hire professional divers to comb the lake bottom at all nine beaches and at both boating centers to make sure there are no more spikes.

Seattle Times staff reporter Jennifer Sullivan contributed to this report.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com