The article is devoted to the content of 15 PAHs in the samples of bottom sediments of rivers and canals located in the central part of St. Petersburg (86 samples). The purpose of the research is to determine the concentrations and distribution patterns of PAHs in streams, as well as to compare the obtained data with the results of studies carried out in the mid 90s of the 20th century. The list of studied polyarenes includes naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benzo/a/anthracene, benzo/b/fluoranthene, 3,4-benzo/a/-pyrene, indeno/1,2,3-c,d/pyrene, dibenzo/a,h/anthracene, benzo/g,h,i/perylene. It was found that the surface layer of bottom sediments in the watercourses was characterized by abnormally high concentrations of PAHs. For different watercourses the average content of 15 unsubstituted polyarenes varies from 4246 to 709168 μg/kg. Heavy 5- and 6-cyclic PAHs dominate, their inflow into the sediment is mainly due to technogenesis. The study of the relation between individual PAHs content showed that the main sources of polyarenes were fuel combustion (road and water transport) and oil pollution. A comparison of the data with the results of previous studies (the mid 1990s) showed that sediment pollution in watercourses of the central part of the city for the past 20 years had increased. In order to unify the results of studies of individual PAHs the PAH hazard ratio (RPAH) was proposed. It is calculated by multiplying the index of individual PAH toxicity to its content in the environment (water, bottom sediments or soil). Determination of the coefficient allows organizing data and facilitates the adjoint analysis of the degree of contamination and the hazard of sediments in the space-time correlation. The obtained RPAH values showed a very high level of environmental hazard (pollution) of sediment in the watercourses, especially in the rivers Ekateringofk a, Karpovka, Moyka and Obvodny Canal. Refs 13. Figs 2. Table 4.