Siltation occurs in many ports and navigation channels around the world. Without dredging and other mitigating measures this results in draft restrictions for vessels entering the ports. The necessity to remove sediments can be reduced by changing the current nautical depth defined by 210 kHz survey towards a nautical depth based on a defined density. Within the fluid mud layer the physical properties such as density and apparent viscosity increase with depth. At a certain depth a transition between the liquid and the solid state can be observed. This transition, associated with specific critical density, could be considered as the nautical depth according to the PIANC definition. For obtaining the actual nautical depth, mud density is the easiest and most accurate parameter to measure.