Automatic wet welding technique with local dry space by water jet curtain has proved its high quality of mechanical properties in weld metal. The most important point to keep high weld quality is precise nozzle positioning. The light cutting method by slit laser beam is promising for shape recognition in air condition. Water proof containers for laser emitter and video camera were prepared for underwater seam tracking of weld line in turbid water. A total light path length in turbid water was shortened as far as possible by acrylic windows on laser emitter and video camera to improve image quality. Emitted laser line became dim by scattering through turbid water. However, it was able to detect groove geometry. Good seam tracking can be carried out. Another trial to get cleat image was carried out by ultrasonic beam scanning; groove geometry can be extracted even when the see-through length is less than 15 mm.