The efficiency of natural wetlands for entrapment and concentration of aqueous uranium (U) was investigated in former uranium mining regions in the eastern part of Germany. Hydrogeochemical analyses of sediments, plants, surface and pore waters from selected small-sized wetlands show that U is predominantly accumulated in an environment where sulfate reduction is insignificant. From soil sequential extraction it is known that the bulk of U is retained in moderately labile forms, predominantly as organically bound or acid soluble phases (“specifically adsorbed”). Uranium could be identified by SEM/EDX, indicating that biosorption of U as cation or complex is important. However, the highest U concentrations prevail in Al-rich, inorganic agglomerates of colloidal phases. These agglomerates are as well very often non-specifically adsorbed to organic matter (plant debris, microorganisms) in the soils, promoting indirect biosorption of U.