In response to continental inputs, the aim of this study was to know some major ions contents in Aby lagoon waters, according to seasons and in relation to temperature, salinity and pH. To do this, concentrations of major ions such as (sodium (Na +), potassium (K +), calcium (Ca2+), magnesium (Mg2+) and sulphates (SO42-) of Aby lagoon waters are determined, according to seasons and in relation to temperature, salinity and pH. From September 2007 to July 2009, during monthly sampling campaigns, temperature, salinity and pH of lagoon’s waters were measured, in situ, at twenty (20) stations distributed along lagoon. Water samples were taken at these stations, at the depth of 0.2 m below the surface, to determine in laboratory, concentrations of major ions using standard methods (Atomic Absorption Spectrometry methods for sodium, potassium, calcium and magnesium and Nephelometric method for sulphates). Seasonal variations of sodium, potassium and calcium concentrations are proportional to temperature, salinity and pH. These ions are under influence of oceanic waters inputs. In contrast, magnesium and sulphates are under anthropogenic influence, these concentrations are not proportional to temperature, salinity and pH. There are significant seasonal differences between major ions concentrations of waters from one season to another. Aby lagoon is under strong anthropogenic influence.