For the first time, we ventured out to the sea to research and study to what degree reefs along the coast of Fukushima is contaminated. Captain Ishii and his CHOEIMARU accurately took us to reefs located about 8 kilometers south of the Fukushima Daiichi Nuclear Power Plant. The points at which we dropped our detector are shown in the map below. From the obtained γ-ray energy spectra, it is confirmed that radioactive cesium still remains at the bottom of reefs. We found, however, that the cable (20m) which connected the detector with the personal computer on the boat was too short to make up the drift of the boat caused by unpredictable wind and current. The obtained data, therefore, should be regarded as an average value over a line on which the detector was dragged by our boat. We shall replace the signal cable and the detector handling rope with longer ones in order not to be dragged by the drift of the boat.