The current study is a part of complex research for establishing new fast and reliable methods for water pollution control. The subject of the study is three anthropogenically affected reservoirs (Kardzhali, Studen Kladenets, and Zhrebchevo), compared with the control - non-polluted one (Vacha Reservoir). Fontinalis antipyretica Hedw. was used as a biomonitor and mossbags stayed for 30 days in the dams. The micromorphological characteristics of cells in the stem and twig leaves of the gametophyte of F. antipyretica were studied by using a light microscope (CETI, Magnum T Trinocular, magnification 400x. A proven increase in the number of cells was registered (significance level between 99% - 99.9% according to Student t-test), both on the branch leaves (for all three affected reservoirs) and the stem leaves (for Zhrebchevo Reservoir). In parallel, a reduction was recorded in the size of cells, mainly in terms of their width, as a result of the anthropogenic pressure. The twig leaves showed higher sensitivity to water pollution than the stem leaves. In conclusion, Fontinalis antipyretica, in particular the number of twig leaf cells and their width, can be used as suitable micromorphological markers in biomonitoring studies of water basins.