  We introduce an effective action for non-dissipative magnetohydrodynamics. A
crucial guiding principle is the generalized global symmetry of
electrodynamics, which naturally leads to introducing a "dual photon" as the
degree of freedom responsible for the electromagnetic component of the fluid.
The formalism includes additional degrees of freedom and symmetries which
characterize the hydrodynamic regime. By suitably enhancing one of the
symmetries, the theory becomes force-free electrodynamics. The symmetries
furthermore allow to systematize local and non-local conserved helicities. We
also discuss higher-derivative corrections.
