Abstract: A problem of remote counting of bubbles and fishes in shallow waters is complicated due to strong reverberation. Traditional way to solve this problem is the use of narrow acoustic beams and short pulse signals, but it is not applicable for all the situations, in particular, in rivers. Reverberation can be suppressed by methods of nonlinear acoustics, since signals scattered by nonlinear targets contain frequencies which are different from primary emitted ones. Bubble-like objects (free bubbles or swimbladder fishes) have strong nonlinear responses. In the present paper a difference frequency method of counting of bubble-like objects is theoretically considered. Since such a nonlinear scattering is resonant bubble and fish sizing becomes possible. For moving targets nonlinear acoustic response exhibits a specific frequency shift, which can be used for velocity estimation.