  We argue that a close analog of the axial-current anomaly of quantum field
theories with fermions occurs in the classical Euler fluid. The conservation of
the axial current (closely related to the helicity of inviscid barotropic flow)
is anomalously broken by the external electromagnetic field as $\partial_\mu
j_{A}^\mu = 2\,\bf E\!\cdot\! \bf B$ similar to that of the axial current of a
quantum field theory with Dirac fermions such as QED.
