Nishikawana is a boat-access dive area at the southern tip of Tateyama on Chiba's Boso Peninsula, shaped by rocky reef, sand, and a V-shaped valley. Strong tidal flow feeds dense fish life, with large groupers, wrasse, grunt schools, turtles, and seasonal ray sightings. It is a site to plan around sea state and current so you can get the best balance of terrain, visibility, and fish action.