The rivers are in some circumstances part of the ground battlefield. Microseisms induced at the riverbed or ground at the
river surrounding might be consequence of military activities (military ground transports, explosions, troop’s activities,
etc). Vibrations of those fluid-solid structures are modeled in terms of solid displacement and change of fluid pressure.
This time varying fluid pressure in river, which originates from ground microseisms, is possible to detect with
hydrophones. Therefore, hydroacoustic measurements in rivers enables detecting, identification and localization various
types of military noisy activities at the ground as and those, which origin is in the river water (hydrodynamics of water
flow, wind, waves, river vessels, etc). In this paper are presented river ambient noise measurements of the three great
rivers: the Danube, the Sava and the Tisa, which flows in north part of Serbia in purpose to establish limits in detection
of the ground vibrations in relatively wide frequency range from zero to 20 kHz. To confirm statement that the river is a
part of ground battlefield, and that hydroacoustic noise is possible to use in detecting and analyzing ground microseisms
induced by civil or military activities, some previous collected data of hydroacoustic noise measurement in the rivers are
used. The data of the river ambient noise include noise induced by civil engineering activities, that ordinary take place in
large cities, noise that produced ships and ambient noise of the river when human activities are significantly reduced.
The poly spectral method was used in analysis such events.