A water-soluble dye used to test ocean currents was poured into rivers in urban and rural settings, turning the rivers green. Carried along by the currents, the dye radically changed the appearance of the rivers and their surroundings. This video documents ‘Green river’ in Tokyo in 2001; other locations for the intervention are Bremen, Germany, 1998; Moss, Norway, 1998; The Northern Fjallabak Route, Iceland, 1998; Los Angeles, 1999; and Stockholm, 2000.