Résumé : Microflora of marine waters and sediments play a significant role not only in the course of natural changes and circulation of elements in this environment, but can also be a decisive factor during erosion processes of various submerged objects or structures such as wrecks, sunken objects, pipelines, etc. The bacteria which have a significant influence on corrosion processes include aerobic and anaerobic sulfur bacteria as well as iron bacteria. Particular importance is attributed to sulfide reducing bacteria (SRB) which occur in waters, bottom sediments, creating biofilms on metal surface, and may start a process known as microbial induced corrosion (MIC). The occurrence of these bacteria and their populations indicates potential and intensification of corrosion processes. The aim of the study was to determine the number of microorganisms from various groups in the Baltic Sea sediments, especially those that are active in biological corrosion processes. This data can be used for a study comprehensive of corrosive processes in the marine environment, and as a result, to carry out a real assessment of the risks arising from the release of toxic substances into the environment from conventional and chemical weapons lying on the bottom caused by progressing corrosive processes, including biological corrosion. The article presents the results of research on the presence and accounts of microorganisms in bottom sediment samples taken from the dump sites of chemical and conventional ammunition in the Baltic Sea. Particular attention was paid to halophilic and halotolerant bacteria due to their significant contribution to both corrosion and decomposition processes of CWA and explosives, particularly in the saltwater environment. There were high and quite similar numbers of mesophilic, psychrophilic and halophilic bacteria in the studied samples, while significantly smaller numbers of anaerobic bacteria. The amount of mesophilic bacteria ranges from 6.42*103 to 2.85*107, on average 4.5*106 in 1 g DM, psychrofilnych od psychrophilic from 5.73*103 in1g DM to 4.11*107 in 1 g DM, on average 6.44*106 in 1 g DM, natomiast dla halofilnych od whereas for halophylic from 4.09*102 to 5.60*107, on average 5.83*106 in1g DM. The numbers of fungi were at a much lower level i zawierały w przedziałach od and ranged from 4.65*101 to 8.08*102, on average 2.63*102 in 1 g DM. mesophilic fungi and from 0 to 1.60*103, on average 3.58*102 in 1 g DM for psychrophilic fungi. The presence of sulfide reducing bacteria (SRB) was also detected in large populations, especially when they were isolated by means of the medium prepared with seawater (from 9.72 to 5.36*102, on average 2.52*102 in 1 g DM), which indicates their adaptation to the saline environment and promotes of biological anaerobic processes, including corrosive processes. No significant amounts of iron bacteria were found, probably due to the small amount of oxygen in the sampling area. The small number of iron bacteria indicates that primarily anaerobic sulfide reducing bacteria (SRB) have the major part in the microbial corrosion phenomena.