Abstract: Water transparency is a primary indicator used to evaluate the status of marine ecosystems. Although a subjective measure, Secchi Depth (ZSD) is one of the “oldest” and most widely used optical parameters in studies that focus on surface water clarity, with probably millions of observations available in the last century. As recent satellite observa-tions do not cover such extended periods from the past, a comprehensive understanding of the spatio-temporal dy-namics of water transparency requires consistent historical data. In this regard, the present study aims to integrate in-formation from archives of in situ ZSD measurements available for the entire Black Sea. Several potential sources were investigated. Among them, two were identified to have historical measurements of ZSD in the Black Sea, SeaDataNet and Black Sea Ecosystem Processes and Forecasting / Operational Database Management System (NATO SfP ODBMS). A database with all available observations was aggregated for this study, containing a total of 5100 records between 1960 and 2016. The analysis of the spatial variability of ZSD was performed based on a square grid of 30 km x 30 km covering the entire Black Sea region. For each cell, statistics such as the average and the number of ZSD measurements were calculated. Moreover, the spatial and temporal homogeneity of the in-situ observations are assessed and dis-cussed.