1) Japanese authorities have been monitoring seawater offshore of Fukushima to measure contamination from the Dai-ichi nuclear power plant. Samples were taken at increasing distances of 30m, 330m, 10km, 20km, and 30km offshore. 2) Higher levels of radioactive iodine-131 and cesium-137 were measured closer to the discharge points, with concentrations decreasing further offshore due to dilution and dispersion by ocean currents. 3) Concentrations 30km offshore were up to 3-4 orders of magnitude higher than historical levels measured in 2005, but were decreasing over time, while concentrations 330m from the plant were up to 3 orders of magnitude higher than 30km offshore.