This article presents the initial hydrochemical status of the Almonte-Marismas aquifer system in 1966 – before agricultural intensification. The investigated aquifer is of critical importance for the groundwater dependent Doñana wetland areas of the National and Natural park of Doñana (SW – Spain). The analytical database involves 158 samples collected in 1966 by the Food and Agriculture Organization (FAO) and the Geological Survey of Spain (IGME), including electrical conductivity, hardness, chloride, bicarbonate, sulphate, calcium, magnesium, sodium, and potassium in groundwater that generate information about the initial hydrochemical state before the intensification of agricultural activity. These historical data existed as hardcopy lab reports and were introduced into a MS Access database. The parameters EC, Cl, SO4 and K of the year 1966 show a variety of spatial patterns before intensification and suggest five different types of influence: (i) natural lagoon systems, (ii) creeks or rivers, (iii) irrigated areas, (iv) urban areas, and (v) marshes. The results suggest that anthropogenic activities such as fertilizer use, domestic activities and wastewater in surface streams downstream of urban areas are responsible for elevated parameter values in most of the observation points, although their specific contributions cannot be determined based on the available data of 1966. In the marshes (north) area, apart from fertilizer use elevated geogenic salinity may also contribute to high parameter concentrations for intensive irrigated crop cultivation and proximity to the Guadalquivir River.