  We present theoretical and numerical evidence to show that self-defocusing
nonlinear optical propagation can be used to compute Euler fluid dynamics and
possibly Navier-Stokes fluid dynamics. In particular, the formation of twin
vortices and the K\'arm\'an vortex street behind an obstacle, two well-known
viscous fluid phenomena, is numerically demonstrated using the nonlinear
Schr\"odinger equation.
