The amoeba Acanthamoeba castellanii is a protozoan belonging to the genus Amoebae. This amoeba lives freely in nature; on land and in water. Most species are so-called opportunistic pathogens, however, some species can still cause infections, especially in animals and immunocompromised individuals. Acanthamoeba species are dangerous because they can cause diseases such as encephalitis and amoebic keratitis. Acanthamoeba species host numerous intracellular pathogens such as bacteria of the genera Legionella, Mycobacterium, Chlamydia, and Francisella. Numerous studies have shown that Francisella reproduces within amoebae such as A. castellanii, and therefore this protozoa is considered important in the transmission of tularemia, especially through spring and surface waters. Through evolutionary mechanisms, many species of bacteria have developed the ability to survive within amoebae. The ability of F. novicida to survive and multiply within amoebae is very important for its survival in the aquatic environment. The aim of this study was to examine the influence of the amoeba Acanthamoeba castellanii on the number of bacteria in water from river of Gorski kotar - the river Čabranka. Certain concentrations of amoeba A. castellanii and bacteria F. novicida were added to the samples. To one of the samples was inoculated only amoeba A. castellanii, to the second sample was inoculated only the bacterium F. novicida, and to the third sample were inoculated both amoeba A. castellanii and bacteria F. novicida. The number of bacteria between the three different types of samples was monitored over a period of 10 days. The number of amoebae A. castellanii was determined using a Neubauer chamber and invert microscope, and the number of other bacteria was determined by membrane filtration and by planting on nutrient media. After the obtained results for each of the individual types of samples, the results were statistically processed and then compared with each other. It was concluded that the amoeba A. castellanii had no effect on the number of other previously present bacteria in the samples. The results of the research show that for amoebae is more suitable enviroment when they are found alone in a sample of the river Čabranka, than when they are found together with the bacterium F. novicida, while F. novicida survives better when is in the sample along with amoebae. It was also found that the bacteria the least survives in a sample of water to which only F. novicida was previously added. According to the document „Uredbi o kakvoći voda za kupanje“ , the river Čabranka did not show a satisfactory criterion due to the excessive number of intestinal enterococci. the The river Čabranka is not a suitable medium for the growth of bacteria such as C. perfringens,E. coli and fecal coliforms. On the fourth day after inoculation (day 4), the presence of A. castellanii was not recorded in any of the samples.