[en] The aim of the note is to supply a new and very simple formula for the conserved densities and to show that the Benney's long wave equations admit a standard Lax representation widely used in the ''inverse scattering method'' of solving wave equations. The system of equations is shown to possess an infinite number of conservation laws. It is also demonstrated that the Benney's equations admit the construction of Hamiltonian systems with Lax-type representations. A new type of universal conserved densities is introduced