Gallocanta is the largest well-preserved saline lake in Western Europe, included in the Ramsar List. Associated with its shallow morphology, the lake undergoes strong variations in its water surface extent along time that condition the habitat distribution and the ecological functions. Data on the morphology of the lake and its hydrological variations along time may be of paramount ecological importance for the managers of this natural space. Even though its interest for research and management purposes, no accurate and robust dataset of this nature covering large periods of time is available. This dataset presents a multi-decadal mapping with a sub-weekly frequency (2-5 days) of the contour of the Gallocanta Lake (NE Iberian Peninsula) along the period 1984-2020 (1043 dates with information). The shoreline position appears continuously defined with subpixel accuracy from the freely-available images acquired by the satellites Sentinel-2 (sensor MSI) and Landsat 5 (TM), 7 (EMT+), and 8 (OLI) by applying the extraction system SHOREX. The satellite-derived shorelines allow the definition of the surface of the lake and are combined with a digital elevation model to assign elevation values to the points defining each shoreline. This allows deducing the mean elevation of the water level and the volumetric changes for those same dates. This data package constitutes a valuable source of information for carrying out robust analyses of the trends of the lake along decades, as well as its response to individual rainfall events.Read less <