The heavy metal bismuth (Bi) is attracting increasing interest for its wide range of applications, from industrial processes to medicine. Given the foreseeable increase in its use, the occurrence of Bi in the environment is expected to increase. There is a lack of information on the impact of this metal on biota, especially for the aquatic ecosystem. In this regard, an experimental study was performed under controlled conditions to assess the effects of Bi on two bioindicator species of the freshwater compartment, namely plants of Lemna minor L. (Lemnoideae) and individuals of Echinogammarus veneris (Heller, 1865) (Amphipoda, Gammaridae). A 7-day assay in L. minor fronds exposed to Bi nitrate in the range of 0–242 mg L− 1 showed no effects of the metal on biometric and physiological endpoints (spectral reflectance indices and chlorophyll fluorescence parameters). In parallel, E. veneris individuals were treated with Bi nitrate (0–242 mg L− 1 ) for 24 h to assess genotoxicity by comet assay. The results showed significant Bi-induced DNA damage in gammarids even at the lowest Bi concentrations tested. The analysis of Bi content revealed the high capacity of both species to accumulate the metal in their tissues, demonstrating the ability of L. minor fronds to tolerate the presence of a relevant amount of Bi in solution, whereas E. veneris individuals showed a remarkable sensitivity to the presence of the metal. The effects of Bi observed in the two aquatic organisms represent the first evidence of a species-specific toxic action of this metal in the freshwater ecosystem.