Bardawil lagoon surface, bottom and interstitial waters from two cores were analysed for Na, K, Ca, Mg, Cl, SO 4 and HCO 3 . Lagoon surface and bottom waters are shown to be formed through evaporation of normal sea water to concentrations, from sea water salinities to three times sea water salinities. In the interstitial waters from cores penetrating about 60 cms of clayey sediments, the following changes were observed: the chlorinity increased with depth and was nearly doubled in the bottom 20 cms as compared to the top 20 cms of the cores. This string gradient is explained by evaporative sabkha formation in the near past at the site of the Bardawil lagoon, and the subsequent mixing of the highly concentrated brine with less saline lagoon waters. Ca/Cl and SO 4 /Cl are decreased in the interstitial waters and explained by gypsum and CaCO 3 , precipitation and/or by the fact that a sabkha containing highly saline brines occupied the place of the lagoon in the near past. Mg/Cl ratios are higher in interstitial waters. This is explained by ion exchange reactions between the montmorillonite in the sediments and the brines. K/Cl ratios are also higher and explained by dissolution of K-feldspars.