<p>Underground mine ventilation systems are vital for maintaining safe and efficient working environments, yet they are highly susceptible to unexpected changes in subsurface conditions, such as water inflows. When a ventilation system is inundated with water, the resulting situation can be complex, with an often-underestimated impact that is capable of altering airflow patterns, generating pressure fluctuations, and compromising system stability. This study examines the effects of water inflows on the ventilation network at the Sanford Underground Research Facility (SURF), formerly the Homestake Mine in Lead, South Dakota. The research focuses on how cascading water falling within an exhaust shaft influences airflow behavior and overall system performance across multiple underground levels. Real-time monitoring data from Maestro Digital Mine airflow sensors were analyzed alongside water discharge measurements collected during three major inflow events in 2023. Using an adapted fixed pressure equation and Ventsim modeling, the induced pressure differential was estimated at approximately 870 Pascals (3.5 inches of water gauge). Model simulations closely matched field observations, replicating the same conditions that were experienced underground. These findings demonstrate that water inflows can significantly disrupt underground ventilation, emphasizing the need to incorporate air–water interaction mechanisms into mine design, monitoring, and emergency management.</p>