Complex microbial communities from river biofilms might contain microorganisms capable of degrading xenobiotic pollutants such as pesticides (e.g. methomyl, which is commonly detected in rivers). Therefore, this study was used to determine the methomyl degradation potential of bacteria consortia and single bacterial strains acclimatized and isolated from natural river biofilms to provide biomaterials for bioremediation of water that is contaminated with methomyl. Natural river biofilms were culture enriched with methomyl as the sole carbon source to obtain acclimatized bacterial consortia and single bacterial strains. The microbial consortium on the ceramic discs was able to remove 91 % of added methomyl (50 mg l−1) in 7 days. The longer-acclimatized bacterial consortium on loofah sponges removed methomyl more quickly than the shorter-acclimatized consortium, but both had similar removal capabilities (i.e. 92.4 and 92.2 %). This finding suggested that the former might contain more methomyl degraders than the latter. However, after preservation at 25, 4 and −20 °C for 1 or 3 months, the methomyl degradation ability of the bacterial consortia decreased significantly, indicating loss of methomyl degraders during preservation. Three bacterial species were isolated from acclimatized river biofilms, and only one species, identified as Sphingomonas sp., was able to remove methomyl, with a 7-day removal rate of 44.7 % when sugar was added and of 32.5 % when no sugar was added. These results suggested that an additional carbon source might slightly improve the ability of Sphingomonas sp. to degrade methomyl. Acclimatized bacterial consortia have a higher potential for treating methomyl-contaminated water than isolated bacterial species.