• Yellow flag iris (Iris pseudacorus)
  Yellow flag iris is a garden escape from Europe. It was first documented as having spread into natural areas in 1911. Once established, yellow flag iris colonizes in large numbers, forming single species stands that out compete native wetland plants (Hill, 2006). City of Eugene Parks and Open Space staff contracted a specialist to navigate to known populations of yellow flag iris in the Delta Ponds area. The contractor cut live emergent vegetation down to the water line. Seeds were bagged and hauled off site (Integrated Resource Management website). In addition to seed reproduction the plant propagates by rhizome. Rhizome fragments left behind become new plants. Yellow-flag iris has been found in landscaping and at lake margins of developed properties on the Island.

• Purple loosestrife (Lythrum salicaria)
  Purple loosestrife is a large, showy plant that is invading wetlands in the United States and Canada at an alarming rate. It was first introduced as a horticultural plant. Klaus Richter (1994) wetland ecologist working for King County, Washington, writes that infestations can become so dense that they smother breeding and cover habitats for ducks, geese, herons and many other water birds. Purple loosestrife forms impenetrable stands with little food value. The strategy used by Parks and Open Space staff in DeltaPondsPark is to “take out” individual plants before they can establish a foothold. This requires labor intensive pulling and bagging to contain seed escape.

• Water primrose (Ludwigia hexapetala)
  Water primrose is an aggressive South American weed that grows in ditches and ponds. It is a fast grower and reproduces vegetatively and by seed (Hill, 2006). The plants have a massive root system making hand removal extremely difficult. Root fragments left behind resprout. Parks and Open Space staff have been mapping water primrose at the Delta Ponds since 2008 with the strategy of keeping it contained to the pond south of the gravel trail and just north of the new pedestrian/bike bridge as much as possible (Holts, 2012).

Goodpasture Island’s lakes, ponds and sloughs contain invasive aquatic plants that reproduce quickly. They were likely introduced into our area by the dumping of home fish aquariums. In other Pacific Northwest locations they are introduced on the rudders and propellers of recreational boats.

Eurasian watermilfoil (Myriophyllum spicatum)

Eurasian watermilfoil is a submersed aquatic plant from Europe, Asia and North Africa that forms dense mats in nutrient rich ponds and lakes. It shades out other native vegetation and provides poor habitat for waterfowl, fish and other wildlife. It was likely introduced into the U.S. in the 1940’s through release from fish aquariums or escaped from private ponds (Wiedemer and Chan, 2008). It is found at IslandLakes and in the Delta Ponds.

Parrot’s feather (Myriophyllum aquaticum)

Parrot’s feather is indigenous to South America. It was introduced to the US in the late 1800s or early 1900s as an aquarium and pond ornamental. It has escaped into shallow water of ponds, lakes and ditches (DiTomaso and Healy, 2003), and has become a serious weed shading out native vegetation. See it in the Delta Ponds.