Three novel Hydromast stations revealed occasional high-amplitude current and water-level oscillations in the 2.4-km-long navigation channel, with dominant periods of 37 and 19 minutes. The oscillation events reflect resonant long-wave forcing from the open sea. The maximum changes in currents and sea level – 0.8 m s⁻¹ and 0.8 m – are harmful to ship navigation, harbor operations, and coastal management. Approaches for detecting and forecasting strong sub-hourly oscillations are discussed.