This study was carried out on petroliferous wastewaters to define the tolerance threshold to salinity of Eichhornia crassipes (Mart.) Solms, the water hyacinth, in order to achieve effluent treatment Plant yield was inversely linked to salinity and varied from 4.2 to 1.1 g d.wt m(-2) day(-1) for salinities (NaCl) ranging from 2 to 2.9 g l(-1). From 6 g l(-1) there was no production and plants were cankered. Over 8 g l(-1) damage was irreversible. The water hyacinth showed a great adaptability to the effluent salinity. Although the production was low, the results do not exclude a possible use for such wastewater treatment.