This study focuses on the dynamics of copepod abundances and species composition in the upper water column of a marine outfall area Tso-Ying (T-Y) in the boundary waters of the north-eastern South China Sea and the Taiwan Strait as an example. Zooplankton samples were collected in March, June and September 2002. Mean copepod abundance at all stations ranged from a minimum of 9.4 (individuals m⁻³) in March to a maximum of 1685 (individuals m⁻³) in June. A total of 66 copepod species belonging to 31 genera and 19 families were identified during three cruises. Copepod assemblages were dominated byTemora turbinatawhich occurred in >97% samples with a relative abundance of 75.46% combining all three sampling cruises. The ordination diagram derived from non-metric multidimensional scaling separated samples on the basis of season and revealed that different sampling stations clustered differently during each cruise. The second and third most dominant species wereAcrocalanus gracilisandAcrocalanus gibber, representing 1.73% and 1.65% of the total copepod abundance respectively. The outfall area studied here correlates with lower copepod densities represented by a few species that show a higher relative abundance in comparison with non-affected areas. We provide here the first example where plankton assemblages indicate useful information about environmental changes in the course of sewage disposal at a stable outlet site.