Cyanides are compounds commonly used in various industrial processes such as mining and coke production. When released into the environment through wastewater discharge, they pose a significant threat to aquatic ecosystems. Once they enter aquatic organisms, cyanides exhibit high toxicity, disrupting cellular respiration and leading to severe ecological and health risks. Due to their toxic effects, it is crucial to remove cyanides from contaminated water to protect the environment and human health. Cyanide removal from water can be effectively achieved through various chemical and physical water treatment methods, including chlorination and ozonation, as well as various biological methods. Biological methods represent a sustainable and environmentally friendly approach, utilizing the metabolic capabilities of microorganisms to degrade cyanides. Ecotoxicity tests are of great importance for determining the necessity of a particular method. Ecotoxicity tests determine the minimum acceptable concentrations of substances in ecosystems at which they do not have harmful effects. These tests are conducted on test organisms under controlled laboratory conditions. In this study, ecotoxicity tests were conducted using two test organisms – the bacterium Pseudomonas putida and the microalga Chlorella sp. The CFU (colony-forming units) value, growth inhibition, and EC20 and EC50 values were measured. The obtained results indicate a high sensitivity of both test organisms to the presence of cyanides, confirming their suitability for assessing harmful effects.