  We examine the physical implications of the viscous redundancy of
two-dimensional anisotropic fluids, where different components of the viscosity
tensor lead to identical effects in the bulk of a system [Rao and Bradlyn,
Phys. Rev. X $\textbf{10}$, 021005 (2020)]. We first re-introduce the
redundancy, show how it reflects a lack of knowledge of microscopic information
of a system, and give microscopic examples. Next, we show that fluid flow in
systems with a boundary can distinguish between otherwise redundant viscosity
coefficients. In particular, we show how the dispersion and damping of
gravity-dominated surface waves can be used to resolve the redundancies between
both dissipative and Hall viscosities, and discuss how these results apply to
recent experiments in chiral active fluids with nonvanishing Hall viscosity.
Our results highlight the importance of divergenceless, magnetization-like
contributions to the stress (which we dub ``contact terms''). Finally, we apply
our results to the hydrodynamics of quantum Hall fluids, and show that the
extra contribution to the action that renders the bulk Wen-Zee action gauge
invariant in systems with a boundary can be reinterpreted in terms of the bulk
viscous redundancy.
