Moss, Norway
In 1998, Olafur discovered that uranin, a readily available nontoxic powder used to trace leaks in plumbing systems, could dye entire rivers a sickly fluorescent green. Olafur conducted a test run in the Spree River during the 1998 Berlin Biennale, scattering a handful of powder from a bridge near Museum Island. He began introducing the environmentally safe dye to rivers in Moss, Norway (1998), Bremen (1998), Los Angeles (1999), Stockholm (2000) and Tokyo (2001) — always without advance warning. He first achieved international prominence with "Green river", which initially made Stockholm pedestrians concerned that the city's water had been tainted.