## 1 Introduction  
In recent years, there has been an unabated upward trend in the consumption of antibiotics. They are widely used not only in medicine but also in veterinary medicine, animal husbandry and aquaculture [1; 2; 3]. Antibiotic residues enter the environment both in metabolized and unchanged form [4; 5]. They are detected in surface and groundwater, bottom sediments, and the soil environment [6; 7; 8]. Such micropollutants are often not effectively removed in the wastewater treatment process, which increases the likelihood of their release into the environment [6; 9; 10]. The effluents from the wastewater treatment plants contain up to 1 mg/L of antibiotics such as \(\beta\)-lactams, macrolides, fluoroquinolones, tetracyclines, sulfonamides and trimethoprim [11]. Antibiotics entering waterways negatively affect aquatic ecosystems. Experiments conducted in model aquatic systems have shown detrimental effects on the population of nitrifying bacteria [7]. Antibiotics such as amoxicillin, sarafloxacin, and tetracycline were harmful to the blue-green algae [12]. Levofloxacin and clarithromycin appeared strongly toxic to the microalgae. Metronidazoleae revealed a toxic effect on _Chlorella_ sp. and _Selenastrum capricornutum_[13]. Numerous antibiotics, including sulfamethoxazole and levofloxacin, negatively affected communities of water macrophytes [14]. It has also been shown that clarithromycin can be harmful to freshwater invertebrates, impairing their behavior, reproduction, growth, and survival of early life stages [7]. There are also data supporting the ecotoxicity of antibiotics to fish and fish embryos [10]. One of the main effects of environmental pollution with antibiotics is the appearance and development of antibiotic-resistant bacteria [11; 15]. The sources of this pollution can be diverse. A study carried out in Australia found that water bodies near sewage treatment plants were contaminated with antibiotic-resistant _Escherichia coli_. Pig farms have been identified as a source of surface water contamination with tetracycline-resistant enterococci. Resistance genes to sulfonamides, macrolides and trimethoprim have been detected in Japanese rivers [1]. Several antibiotics used as growth promoters (spiramycin, tylosin, carbadox, monensin, and virginamycin) were suspected of being a cause of the cross-resistance to other pharmaceuticals [16]. The mechanisms related to microbial resistance to antibiotics include horizontal gene transfer, the modification of the binding target, the removal of antibiotics out of the cell (active efflux) and the enzymatic degradation and modification of antibiotics [17]. Water bodies used for recreational purposes require special care when it comes to ensuring health and safety. Routine sanitary testing of bathing water does not reflect the full spectrum of potential risks of a microbiological nature. The objects of interest when it comes to potential health risks associated with microbiological contamination of surface waters are usually fecal bacteria, mainly from the _Enterobacteriaceae_ family (_Salmonella_ spp., _Shigella_ spp., _Yersinia pestis_, _Klebsiella_ spp., and pathogenic strains of _E. coli_). _Staphylococcus aureus_ bacteria have also been detected in the waters [18]. Surface water quality regulations do not address the presence of antibiotic-resistant bacteria and drug-resistance genes in the water [18]. In this context, the problem of contamination of recreational waters with antibiotic-resistant microorganisms seems particularly relevant. There is a need to pay special attention to the phenomenon of bacterial resistance to new-generation antibiotics, including those used to treat severe bacterial infections that are difficult to treat. In this research, we focused on the occurrence of bacteria resistant to two frequently used antibiotics--ciprofloxacin and imipenem--in the bathing waters of the Great Rudnickie Lake, one of the popular recreational sites in Poland.