  We suggest the Hamiltonian approach for fluid mechanics based on the
dynamics, formulated in terms of Lagrangian variables. The construction of the
canonical variables of the fluid sheds a light of the origin of Clebsh
variables, introduced in the previous century. The developed formalism permits
to relate the circulation conservation (Tompson theorem) with the invariance of
the theory with respect to special diffiomorphisms and establish also the new
conservation laws. We discuss also the difference of the Eulerian and
Lagrangian description, pointing out the incompleteness of the first. The
constructed formalism is also applicable for ideal plasma. We conclude with
several remarks on the quantization of the fluid.
