The paper presents first description of class 1 integron in an environmental strain of Rahnella aquatilis, a rarely isolated Gram-negative bacterium of the family Enterobacteriaceae. The strain was isolated from the Warta river water, Poland. Class 1 integrase gene was detected by a PCR assay. Sequencing of the integron's variable region showed the presence of a dfrA1-aadA1 gene cassette array. The integron was located in a 54-kbp plasmid that was transferable to Escherichia coli J-53 recipient strain in a conjugation assay. The integron-bearing R. aquatilis strain was resistant to aminoglycosides, penicillins, trimethoprim, sulfamethoxazole, and trimethoprim/sulfamethoxazole. This paper confirms that water environment play a major role in the spread of integrons and, consequently, antimicrobial resistance, among bacteria of various genera.