PROBLEM TO BE SOLVED: To provide a treatment agent to prevent malodors and dusts of a bottom sediment. SOLUTION: The bottom sediment treatment agent contains (A) lime and (B) water-soluble polysaccharides, wherein 0.5 to 5 pts.mass of the water-soluble polysaccharides is contained in 100 pts.mass of the lime. COPYRIGHT: (C)2013,JPO&INPIT