PHYTOPLANKTON AND HYDROGRAPHY OF THE BAY OF CADIZ (SW SPAIN) FROM APRIL 1986 TO DECEMBER 1988.- Temporal evolution of several physico-chemical parameters (temperature, salinity, pH and dissolved oxygen concentration), nutrients (NH₄⁺, NO₂^-, NO₃^- y HPO₄^2-), chlorophyll a and pheopigments in the Bay of Cadiz are presented. Sampling was carried out at four stations during 1986-1988. The most remarkable feature of hydrological conditions is a large decrease of salinity during 1988. Simultaneously, an increase of chlorophyll a and nutrients has been registered in relation to the previous years. This pattern is related to the infrastructure works carried out on the coast during the past years. Mean annual values of pheopigment concentration ranged from 0.66 - 1.37 mg m^-3 and at one station reached 30% of total chlorophyll pigments.