Nozzle cloggingNozzle clogging is one of the main problems in continuous steelSteel casting, which increases meniscus velocity, causes excessive fluctuations in bath level, and leads to the opening of the slag layer. Due to the importance of producing high-quality steelSteel, this study aims to understand and quantify the detrimental effects of severe nozzle cloggingNozzle clogging on mold fluid dynamics. To address this, an industrial nozzle at the end of its service life was 3D scanned and modeled through numerical simulationNumerical simulation. The real clogging behavior was compared with nozzles with symmetrical reductionsReduction in the lower tubular section, ports, and pool. The results show that the high velocity and wall irregularities of a severely clogged nozzle cause jet rotation, deflection of the jets toward the front mold wall, strong bath-level asymmetries, vortex formation, and slag entrapment on both sides of the nozzle. These effects are not observed in cases with symmetrical reductionsReduction.