16-001014-02A (Ultimate SCMMP)

     Floating weeds
     Floating weeds are unattached, free-floating plants that
     grow on the surface of a water body. They are generally
     characterised by extensive, fibrous root systems that
     bind together, enabling the plant to develop a dense mat.

     Under suitable conditions, floating aquatic weeds
     rapidly form dense mats over water surfaces, reducing
     light penetration and oxygen exchange. The decomposing
     plant material removes oxygen from the water, which
     can result in poor water quality and severe impacts to
     aquatic fauna.

     Small infestations of floating aquatic weeds can be
     physically removed by hand using rakes and floating
     booms. Larger infestations may need to be removed
     using mechanical harvesters or excavators. Physical
     removal is often expensive but also has the advantage of
     removing a nutrient load from the water body, provided
     it is regularly carried out. All removed plant material
     should be relocated away from the water body and
     buried, composted, or disposed to landfill.

     Herbicides are a cost-effective control method when
     dealing with large infestations; however, sinking and
     decomposing vegetation is likely to contribute to water
     quality problems.

     A number of biological control methods have been
     successfully introduced to control floating aquatic
     weeds, including salvinia, water hyacinth, and water
     lettuce. Refer to the plant descriptions for further
     information on specific biological controls.

     Eradication of floating aquatic weeds is difficult. All
     initial control treatments must be followed with vigilant
     monitoring and repeated treatments where necessary.




64                     Maintaining Vegetated Stormwater Assets Version 1