  3+1-dimensional free inviscid fluid dynamics is shown to satisfy the criteria
for exact integrability, i.e. having an infinite set of independent, conserved
quantities in involution, with the Hamiltonian being one of them. With (density
dependent) interaction present, distinct infinite serieses of conserved
quantities in involution are discovered. Clebsch parametrization of the
velocity field is used in the the latter analysis. Relativistic generalization
of the free system is also shown to be integrable.
