Slime from small water-conducting canals in tidal land is sometimes excavated by farmers and applied to the surrounding grassland. The canals are interconnected with rivers near the sea, and nuclear power stations are sited at those rivers. There is a possibility, as a consequence of the tide, that small amounts of radioactive contamination from the rivers will be deposited on the slime in the canals. Therefore, an investigation was made to determine the contamination of grass caused by slime containing 137Cs and 60Co.