We show that the tsunami of November 3, 1994 in Skagway, Alaska was generated by an underwater landslide formed during the collapse of a cruise ship wharf undergoing construction at the head of Taiya Inlet. This event occurred at a time of extreme low tide and was not associated with a regional seismic event or incoming oceanic tsunami. Persistent wave motions with an amplitude of 1 m and a period of 3 min recorded by a tide gauge in Skagway Harbor following the landslide are linked to the formation of a cross‐inlet seiche and quarter‐wave resonance within the harbor. The high Q factor for the harbor (Q ≈ 20) indicates weak dissipation and strong resonance within the harbor.