  Flow coefficients $v_n$ for $n$ = 2, 3, 4, characterizing the anisotropic
collective flow in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, are
presented. They indicate the expected growth of viscous damping for sound
propagation in the quark gluon plasma (QGP) produced in these collisions.
Hydrodynamical model comparisons which include the effects of initial state
geometry fluctuations, highlight the role of higher harmonics ($v_{n, n>2}$) as
a constraint for disentangling the effects of viscosity and initial conditions,
and suggest a small specific viscosity for the QGP. This viscosity is
compatible with that obtained via a newly proposed technique
\cite{Lacey:2011ug} which employs the relative magnitudes of $v_n$ to estimate
the viscosity, and the "viscous horizon" or length-scale which characterizes
the highest harmonic that survives viscous damping.
