  In simple fluids, such as water, invariance under parity and time-reversal
symmetry imposes that the rotation of constituent 'atoms' are determined by the
flow and that viscous stresses damp motion. Activation of the rotational
degrees of freedom of a fluid by spinning its atomic building blocks breaks
these constraints and has thus been the subject of fundamental theoretical
interest across classical and quantum fluids. However, the creation of a model
liquid which isolates chiral hydrodynamic phenomena has remained experimentally
elusive. Here we report the creation of a cohesive two-dimensional chiral
liquid consisting of millions of spinning colloidal magnets and study its
flows. We find that dissipative viscous edge pumping is a key and general
mechanism of chiral hydrodynamics, driving uni-directional surface waves and
instabilities, with no counterpart in conventional fluids. Spectral
measurements of the chiral surface dynamics reveal the presence of Hall
viscosity, an experimentally long sought property of chiral fluids. Precise
measurements and comparison with theory demonstrate excellent agreement with a
minimal but complete chiral hydrodynamic model, paving the way for the
exploration of chiral hydrodynamics in experiment.
