Background Environmental conditions are one of the main drivers of fish species distributions along river networks. In order to anticipate and assess the effect of climate change on the occurrences of fish species, and especially of temperature rising, numerous Species Distribution Models (SDMs) were developed to project the species distribution depending of the gas emission scenario. The idea underlying these models is to relate the occurrence of a given species in stream sections (sites) to the environmental conditions observed in these sites. This assumption is valuable for all statistical methods that were used to define SDMs. Occurrence-environment relationships are then used to predict species presenceabsence under different climatic scenarios. Even if numerous SDMs were used to predict the shift in species distributions and assemblage composition, very often these models were computed over a spatial extent that would reflect only a small fraction of the realized niche of these species. These models should thus over- or underestimate the effect of climate changes because they would extrapolate species occurrences for environmental conditions not taking into account in the calibration data sets. Moreover, very often these models only integrate temperatures and do not consider precipitation. Logez et al. (accepted), developed SDMs for 23 widespread riverine fish species in Europe with the data base of the EFI+ project (14 European countries). These models: consider a great diversity of environmental conditions, were computed on sites not or slightly impacted and integrate both temperature and precipitations through the stream power. These models would be useful to assess the climate change effect on the future distribution of these 23 species. In parallel to the SDMs, some long term studies provide real observations of the climate change effect on river functioning and their consequences on fish populations. The case study of the Traun River conducted over more than 30 years highlights the response of a coldwater species to water warming. Objectives and approach The objectives of these studies were to assess the climate change, both in term of temperature and precipitations, on the future distribution of fish species, but also the uncertainty on the predicted patterns. This is a major concern for water managers to have an idea of the vulnerability of populations to climate change to program restoration measures or to assess the reliability of taken these measures. Four emission gas scenarios, averaged from three global circulation models, were used to predict species distributions at the European scale by 2020–2030 and 2050–2060. For each scenario, the probabilities of presence of each species, in absence of pressure, were computed from the logistic regressions developed by Logez et al. (accepted). These probabilities were compared to a threshold probability (different for each species) and derived into absence-presence. The confidence intervals associated with each expected probability were computed using the Wald’s approach. These intervals estimate the uncertainty around each prediction. Larger this confidence interval is, more uncertain is the species response to global change. In parallel, the case study of the Traun River, central Austria, was used to assess the potential effect of temperature rising on historical grayling populations. This study focus on the grayling populations of section Traun lake outflow downstream. Results Species present various patterns of response to climate change On average, the mean air temperature in July is expected to increase in our sampling sites by 1.7 °C in 2020– 2030 and by 3 °C in 2050–2060, whereas the warming between these two periods is less pronounced for mean air temperature in January (Table 1). Precipitations are expected to decrease by 16 mm in 2020-2030 and by 8 mm in 2050-2060. The patterns of responses to climatic shifts are highly variable between species, but the greatest changes will occur by 2050–2060. For cold- and coolwater species such as brown trout and its associated species, grayling and Atlantic salmon, the number of locations will suitable habitat would be greatly reduced. Other species such as nase, dace and soufie will face both local extinctions and new colonisations suggesting a shift of their distribution by 2050–2060, while climatic conditions will become highly suitable for bleak. Uncertainty could blur the pattern of responses For some species the uncertainty around the probabilities of presence was so high that depending of the confidence interval limit opposite patterns of response to climate change could be predicted (Table 3). This is the case for instance of nase, for which local extinctions are mainly predicted when using the lower limits of the confidence intervals or an important expansion of its distribution area when considering the upper limits. Low uncertainties are associated with species with a marked response to climate change such as bleak and Atlantic salmon. Grayling populations will suffer from climate change Over the period 1976-2008, the water temperature in August of the section Traun lake outflow downstream, increase by 2.2 °C on average. In parallel with this warming the abundance of the grayling sharply decline, replaced by species such as barbel (Figure 2). For this river, the global change was followed by a shift of assemblage composition toward species with warmer thermal ranges. At a measuring point temperatures of 24 °C and more are reached constituting a substantial source of stress for the grayling. Implications Although restoring rivers from a societal and ecological point of view a good thing, water managers must take into account the climate change in their decision process to restore rivers. The restoration programs could be inefficient in regards of the prior objectives, not because of inappropriate measures but because climatic conditions will overwhelm the limiting effect of human pressures and limit the occurrence of the target species. The case study of the Traun river clearly show that a return to the historical fish assemblages is impossible and can´t be reached for instance by fish stocking at the lake outflow section.