In this paper we examine ways Sahelian floodplain fishers have adapted to the strong environmental variations that have affected the region in the last two decades. We analyse their vulnerability and adaptive capacity in the face of expected changes in rainfall combined with the predicted effects of dam construction. Data from the Inner Niger Delta in Mali were used to show that fishers were highly sensitive to past and recent variations in the hydro-climatic conditions. Moreover, it appears their traditional livelihood strategies, although diversified, sophisticated and well suited to historical conditions, offer a limited set of options to adapt to increased environmental constraints. For fish-dependent households that have adopted a mixed set of activities through farming, the high seasonality and constraints characterizing both their main activities (fishing and farming) does not allow switching between activities. For those households that undertake seasonal fishing migrations, there is little opportunity to modify migration routes or find new settlements sites inside the delta because of the high population density in this area. In sum, although the adoption of diversified and spatially discrete patterns in livelihood activities is often presented as a strategy to reduce vulnerability, such a strategy does not appear sufficient to allow fishers of the delta to successfully face the increasing constraints associated with the changes in hydro-climatic conditions. In such a context, fishing communities will be driven towards more drastic strategies of adaptation and/or coping such as switching to new activities based on agricultural innovations or emigration from the delta. Both strategies present many hazards, particularly in the absence of supportive public policy.