<p>Laboratory uptake and depuration kinetics of ¹³⁷Cs were determined in freshwater green filamentous algae <i>Spirogyra</i> sp. and macrophyte <i>Hydrilla verticillata</i> by using the radiotracer technique. This study provides the first comprehensive comparative analysis of two distinct groups of freshwater plant, free floating algae and a submerged vascular plant, that accumulate radioactive ¹³⁷Cs over time. The results showed that both plants take up ¹³⁷Cs from water in direct proportion to its dissolved concentration during the experiment. At equilibrium, the concentration factors were found to be 4.80 ± 0.03 (mL g⁻¹) and 3.15 ± 0.06 (mL g⁻¹) while uptake rate constant <i>k</i>_<i>u</i> was 0.58 ± 0.09 (d⁻¹) and 0.21 ± 0.04 (d⁻¹) for <i>Spirogyra</i> sp. and <i>H. verticillata</i>, respectively. Depuration kinetic parameters indicated that most of the radiocesium was rapidly lost from plants during the first days of depuration, and only 20–40% of ¹³⁷Cs was retained in both plants at the end of the experiment. The depuration rate constants (<i>k</i>_<i>e</i>) and the biological half-lives (<i>T</i>_b1/2) of ¹³⁷Cs were observed to be 0.16 ± 0.01 (d⁻¹) and 0.09 ± 0.08 (d⁻¹) and 4.29 ± 0.01(d⁻¹) and 7.70 ± 0.04 (d⁻¹) for <i>Spirogyra</i> sp. and <i>H. verticillata</i>, respectively. Differences in ¹³⁷Cs concentration between both species growing under similar environmental conditions suggest that the uptake rate of ¹³⁷Cs is mainly influenced by plant morphology. The results presented in this study suggest that both <i>Spirogyra sp</i>. and <i>H. verticillata</i> could serve as suitable bioindicators for monitoring ¹³⁷Cs contamination in freshwater systems.</p>