The state has given Friends of Vancouver Lake the OK to use its preferred herbicide to treat milfoil infestation, the group announced Sunday.The announcement came during a fundraiser at the Vancouver Lake Sailing Club, part of the Friends’s ongoing efforts to eradicate the aquatic invasive weed. After surveying the lake for two days in early July, ProcellaCOR — favored over other herbicides because it will prevent an extended closure of the lake — will be placed in the lake July 16, said Larry Cassidy, the group’s chairman.“We’re going to be able to use the best herbicide,” Cassidy said. “This is a big deal for Vancouver. This is a big deal for Clark County. We need to work not just this year but for the next few years.”Eurasian milfoil started choking the shallow lake a couple of years ago. The cause is unknown, though some have surmised that it may have been introduced by a boat or through a flushing channel connected to the Columbia River.“I had a pit in my stomach because I knew what that meant,” said Philip Parshley, the sailing club’s commodore, about the first time he noticed the weeds.Milfoil currently covers 20 percent of the lake, primarily located near shorelines, and could engulf it by 2022 if not treated, according to the Friends group. The tangles of vegetation would render the lake unusable for rowing, sailing and other recreation. It also warms the water, chokes fish habitat, drives out native plant species and makes swimming dangerous.