PURPOSE: To treat a sludge with a high water content inexpensively and efficiently by a method wherein lime or the like with low density and high water absorbing capacity is firstly scattered over a sludge accumulated on the sea bottom or the like and, thereafter, a sheetlike net is covered and, moreover, sands or the like are scattered thereover.

CONSTITUTION: Over a whole surface of a sludge polluted with a harmful substance such as heavy metals accumulated on a pond bottom or sea bottom, firstly, a substance with a low density, very fine particle size, high water absorbing capacity as well as sticking property after it has absorbed water such as lime or gypsum is scattered. Subsequently, if a sheetlike net is covered, it is precipitated into a scattered layer by its own weight and interposed within the scattered layer and combined with the water absorbing sticky layer. Thereafter, a substance with relatively large particle diameter and high water permeability such as sands is scattered to form a moisture evaporating and loading layer. Thereby, a sludge with a high water content is treated effectively.