About three weeks ago, a lake user stepped on a sharp object in Green Lake, a popular Seattle lake. Soon a number of additional spikes were detected. Divers then moved to the lake and found even more. The media speculated that this was a criminal act and the police mobilized to investigate.
Upon seeing news coverage of this, Aquatechnex employees remembered that Dupont had produced a milfoil bottom or benthic barrier kit that used stainless steel pins that looked identical to those the divers were bringing up on TV. We contacted the parks department and helped them identify and locate records necessary to put this mystery to rest.
As our company is responsible for managing Eurasian Milfoil at a number of Seattle beaches, the Department asked us to mobilize our diver teams to clear Green Lake and remove these from other sites in the City where they have have been placed. We quickly discovered additional beached with these pins. In those cases however, the pins were still in very good shape and posed no threat to swimmers.
Green Lake has been subject to two applications of Aluminum Sulfate in the past few years to remove phosphosus and help manage algae blooms. This material is extremely corrosive to metal, and it is our opinion that these treatments had a lot to do with the failure of this pin system in Green Lake.
For more information google “green lake spikes” and you will see a number of related stories. This should serve as a reminder that benthic barriers need ongoing maintenance.