For rehabilitating sea floor around and under a potentially environmentally hazardous area such as shipwrecks including hazardous cargo or deposits of environmentally hazardous material, it may be used a layered bottom structure that may be placed on top of such polluted sea floor in lakes and oceans at and about areas, pockets or stores (1) of environmentally hazardous material(s), wherein said environmentally hazardous material(s) is in danger of leaking out to the surroundings. The layered structure comprises at least one layer of a mass on top of said area of environmentally hazardous material(s) including a viscous material (3,9) comprising sludge/earth/clay and including fine-graded particles impregnated with reactants that are able to react with the relevant environmental hazardous material(s) and bind and/or render these harmless. It is also disclosed a process for distributing such a layered structure.