Invasive sea lamprey (Petromyzon marinus) is a fish parasite that has damaged the Great Lakes ecosystem. In-stream barriers that prevent upstream passage during migration can help reduce populations of sea lamprey. Exploring their swimming kinematics will help us understand how lamprey navigate across barriers at various water depths. I recorded attempts of sea lampreys to cross wetted ramps varying in water depth from 1 to 7 cm and used video analysis to examine their swimming mode. I found that at the shallowest depth, amplitude and frequency of body undulations were increased, but swim speed was not. I conclude that swimming capacity was reduced in the shallowest treatment. My findings suggest that a lamprey barrier with shallow water could block sea lamprey but allow native fin-fish species to pass upstream.