<p>Endemic plants on gravel bars along the river maintain populations in a balance between the creation of habitat by the formation of bare land in floods and the loss due to runoff, burial, and overgrowth of competing plants. In the middle reaches of the Tama River, restoration actions for the endangered plant Aster kantoensis Kitamura (AKP: Aster kanoensis Project) have been carried out for 20 years in partnership of citizens, public administration, and researchers. AKP began actions to reinforce the regional population in KUSABANA area (KUSABANA population, commonly known as once the largest population in the Tama River, which disappeared in 2015) in the experimental gravel riverbed developed downstream of KUSABANA population in 2002. The new local population in the sowing area with high relative height, expanded to the area with low relative height. The population in the sowing area, decreased due to the overgrowth of competing plants, so actions of weeding competing plants began in 2006. Most of the land in the area with low relative height, was bare due to a large-scale flood occurred in 2007. The individual settlement by wind dispersal of seed was promoted and the range of local population was expanded. Since 2015, the number of flowering individuals has decreased to less than 80　due to further overgrowth of competing plants in the sowing area. Furthermore, the number in the area with low relative height also, has decreased due to the small-scale floods with no bare ground. An unprecedented large-scale flood in 2019 caused the disappearance of all individuals in the experimental area. Accordingly, preserved seeds were reintroduced in 2020 and 2021, and 211 of flowering individuals were observed in the fall of 2021. Since 2017, sowing actions has been carried out in suitable areas other in addition to the experimental area. The rosette/flowering population ratio, which represents the growth capacity of the population, reached its maximum in the second year after bare land formation and began to decline in the third year, so the activities to remove competing plants for maintaining the population became overwork. There are also risks of extremely large flooding that cause the loss of entire local populations. For these reasons, rather than artificially baring a small area of a riverbed and introducing a population and maintaining it by weeding, it may be more realistic to sow it flexibly in a suitable habitat that is scattered throughout the riverbed and changes its distribution over time. AKP has been revising its activities according to the river environment and the growth conditions of the A. kantoensis with consolidating the information provided by public administration on river management plans, the knowledge of researchers to judge the growth status, and the work capabilities of citizen volunteers. In an ever-changing river environment, the organization like AKP with continuity and adaptability is effective.</p>