Serra da Estrela is Portugal's mainland highest mountain, with distinctive geological, climatic and geomorphological characteristics which play a key role on surface and groundwater resources. These mountains have the largest set of glacial ponds of Portugal and are scarcely studied. Besides, there are concerns of possible impacts of the use of salts in road de-icing on ponds' biotic communities. This research intends to characterize the hydrology of five Mediterranean alpine ponds and assess

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... eir planktonic communities. The biotic index proposed by the Water Framework Directive for lentic systems was used to check its applicability to these systems. Sampling was conducted monthly from June to November 2015 alongside with hydrological characterization. Water parameters and nutrients' content were quantified. Phytoplankton and macrozooplankton were identified. Ponds' water level is controlled by precipitation (input) and evaporation, infiltration and streamflow (output). Ponds were in good ecological quality. However, the current ecological assessment tools proposed by the WFD for lentic systems do not fit alpine ponds, showing a gap in the current methods. Salts used for road de-icing did not impact the communities and the ecological state of ponds. Phytoplankton was dominated by Cyanobacteria, Dinophyceae and Bacillariophyceae; Cyclopoida was the most abundant zooplanktonic group. For macrozooplankton, RDA shows association between cladocerans and phosphorus content. Phosphorus changes promoted shifts in zooplankton, what may be of major concern from a conservation point of view, once alpine ponds and its species are still mostly unknown. Efforts should be done to develop tools to classify aquatic ecosystems from harsh environments.