<p> This study, conducted at M River Park in Moriyama city, Shiga prefecture, was undertaken to elucidate aspects of mutual collaboration between residents' associations and individuals enjoying environmental conservation in their daily lives in a suburban area. The M River, built for irrigation before the eighteenth century, is currently managed by the residents' association and a few individuals who have managed it for pleasure and fulfillment. Officials of the residents' association have been predominantly longer-term residents. They are self-employed people from families with generations of community residence. In contrast, the core members of the individuals are retirees who have been residents since the 1970s. Faced with environmental problems, particularly pollution and floods, related to the waterways, the residents' association members have started waterway cleanup operations as countermeasures. The motivation of the individuals is considerably different. They manage waterways almost every day to maintain the habitat for fireflies or water flowers that make their life more enjoyable. Although no formal discussion or cooperation among them has been observed, their activities are mutually complementary. The residents' associations can achieve environmental conservation indirectly by forming complementary relations with the individuals conducting environmental conservation activities. However, the individuals are able to continue controlling their activities through complementary relations with the residents' associations. Through this loose mutual collaboration, residents who understand both longer-term residents' and retirees' differing senses of values have played a key role as mediators between them.</p>