Submarine groundwater discharges (SGD) in the SW Peloponnesus are ubiquitous, but the Kalogria Bay underwater spring is surprisingly permanent, and strong, according to previous information. During 2006, preliminary investigations revealed the presence of SGDs characterized by high discharges of freshwater (salinity <2). The possibility of potential use of the SGD water for drinking purposes motivated a multi-disciplinary study of the spring from July 2009 to July 2010. The spring discharges at ~26 m depth, at the section of two faults, which expose the limestone bedrock to the surface of the seafloor. Monitoring of flow velocity, temperature, and salinity every 30 minutes was achieved by the deployment of a lander, equipped with various sensors, designed and modified accordingly for the purposes of this study. The results have shown high flow velocities (>125 cm s-1), which correspond to a discharge estimate of 4500 m3 h-1. Salinity variations were high, but minimum values ~1-2 were constantly recorded since mid-October 2009, and until the beginning of May 2010, where abruptly salinity increased to values higher than 12. The complex morphology of the seabed at the SGD point, which was covered by a big rock, is probably creating a rather fast mixing of freshwater and ambient high salinity water. Under these conditions, the potential exploitation of the spring water was not justified.