In the article the author describes the Polish specificity of deep dives used in underwater deep-sea works. The article briefly discusses the methods of deep diving used in the world to proceed to underwater works in the Polish offshore zone of 50-90m depth (according to the Act; deep water works are works below a depth of 50m). When discussing these methods, the author describes the technical-organisational and formal conditions and the type of conducted works. It then presents the methodology for evaluating the effectiveness of the main element of deep-sea works, i.e. diving. It provides information on deepsea underwater works on the Baltic Sea carried out by the Department of Underwater Works Technology of the Naval Academy in cooperation with the Polish Navy until 2001 and civil companies to date. On the basis of his own data from underwater deep-sea works, the author presents the methodology of evaluation of their effectiveness from the point of view of deep dives. In his conclusions, he puts forward recommendations for improving the efficiency of such works.