ABSTRACT This study aimed to investigate the REEs’ presence in the rocks and groundwaters of three different aquifers in eastern Crete. The first developsin carbonate rocks, and is a typical unconfined karst aquifer. The second, developsin Miocene conglomerates and sandstones, and is confined by marly formations, whilethe third in the Pliocene conglomerates overlying the Phyllites Formation. Theyare all formed by minerals such as calcite, dolomite, aragonite, anhydride,halite and sylvite, display neutral to slightly alkaline pH and positive to slightlypositive redox values. The karst aquifer is of Ca-Mg-HCO3 water type, while near the coast Na+ and Cl− are also involved due to seawater intrusion. In the other two aquifers, complex hydrochemical types prevail suchas, Ca-Mg-Na-HCO3-Cl for the second or Na-Ca-Mg-Cl-HCO3 for the third one. ΣREEs concentrations range between 64 and 1,671 ppm for rocks, 45 and 120 pptfor 0.45 μm filtered, and 219 and 1,087 ppt for unfiltered groundwater. Thedifferences between filtered and unfiltered samples were attributed to the greatertendency of REEs to be adsorbed on surfaces such as Fe-Mn oxides andhydroxides, some organic substances or particles, colloids, clay minerals, andmicroorganisms, which were removed during filtration. Furthermore, an evidentnegative Ce anomaly in the filtered samples was attributed to the Ce oxidationand removal from the dissolved phase. The Japanese and European shales normalised REE diagrams of all groundwater samples show great similarities attributed to the presence of common major minerals such as calcite, dolomite and gypsum. The positive Eu anomalies were attributed to the dissolution of these common minerals from the aquifers’ bedrock. Finally, the increased concentrations in the unfiltered samples of the porous aquifers were associated with ion exchange processes, while the lower values in certain brackish samples were attributed to colloidal precipitation processes due to the increased salinity.