The major natural factors of the South Evvoikos Gulf are the existence of an almost closed boundary and the increase of the gulf width moving to the other boundary of the gulf; the later favors the communication with the South Aegean Sea and the entrance of the relevant water mass. In their turn, abiotic (salinity, nutrients, particulate carbon, sediments) and biotic parameters (phytoplankton, zooplankton, phytobenthos, macrozoobenthos) revealed a more or less gradual spatial variability between the two edges of the gulf. Pressures on the marine environment by human activities varied spatially, with the majority of industrial and agricultural pollutants discharged in the more confined area, either directly or indirectly by Asopos river. The impact of domestic wastes was detected along all the coasts of the gulf, where human population increases by a factor of three to ten during summer. A large number of mariculture sites are located in South Evvoikos Gulf, as well as three major ports. The environmental status of selected sites of the gulf was estimated by the combination of several ecological indices. Only the more confined area was classified to moderate status, while the majority of the gulf is in good status.