Purple loosestrife (Lythrum salicaria) is a perennial that blooms in midsummer. The upright bushy plants can reach 7′ tall and features pink to purple flowers traveling up a long spike. It grows quickly and crowds out marsh vegetation needed by wildlife for food and shelter. The plant is native to Asia and Europe but has become an established aquatic invasive in the U.S.; you can see it along wetlands, stream banks and by shallow ponds.
In Oregon, specialists have used four biological controls for purple loosestrife with some success: two leaf beetles, a root weevil and a seed weevil.