The present study aimed to determine the fitness of genetically modified microorganisms (GMMs) and their parents in aquatic environment (river water) through the genetic stability and transduction abilities. Two GMMs (RS1, RS2) Pseudomonas aeruginosa strains were used. The results show that the transferred genes were stable up to 15 days in RS1 and 30 days in RS2, but the cfu/ml was decreased. The survival of RS1 was decreased from 2.87x10¹¹ at zero time to 8.9x10² after 15 days, while  the cfu/ml of RS2 was decreased from 9.39x10¹¹ to 6.0x10¹. The fitness of RS2 was higher than their parents. The GMMs were used as a donor to study their transducing abilities in situ by transduction mechanism. GMMs were able to transfer their DNA to other bacterial strain. Transduction frequency was declined from 6.12x10^-8 to 8.2x10^-11 through 20 days for RS1 and from 4.4x10^-8 to 1.6x10^-10 for RS2. No transductants have been detected after 20 days. The abiotic factors that may be effect on GMMs under environmental conditions were investigated under laboratory conditions. UV, pH, ions and temperature have been tested on the survival and transducing ability of GMMs. The remarker effect was observed with acidic pH, trivalent cation (Fe⁺⁺⁺) and 42^◦C. The survival and gene transfer were dramatically decreased.