Water solutions of some dyes produced by Bayer (Isolan Orange S-RL, Isolan Marineblau S-RL, and Isolan Gelb S-GL) were decolourized by the NaOCl/Fe²⁺, HOCl/Fe²⁺, and H₂O₂/HOCl/Fe²⁺ systems. These Fenton-like reactions also show a very good efficiency in lowering COD. The best results were obtained using coagulation initiated by the Fenton or Fenton-like reaction. The oxidation systems used led to better results than in a simple Fenton reaction.