  We consider a p+1-dimensional timelike hypersurface \Sigma_c embedded with a
flat induced metric in a p+2-dimensional Einstein geometry. It is shown that
imposing a Petrov type I condition on the geometry reduces the degrees of
freedom in the extrinsic curvature of \Sigma_c to those of a fluid in \Sigma_c.
Moreover, expanding around a limit in which the mean curvature of the embedding
diverges, the leading-order Einstein constraint equations on \Sigma_c are shown
to reduce to the non-linear incompressible Navier-Stokes equation for a fluid
moving in \Sigma_c.
