Any material (concrete blocks, reeds, wood, dirt, gravel
, etc.) used for the primary purpose of replacing an aquatic
area with dry land or of changing the bottom elevation
of a waterbody. The term does not include any pollutant
discharged into the water primarily to dispose of waste
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.