  We investigate the evolution of rigid bodies in a viscous incompressible
fluid. The flow is governed by the 2D Navier-Stokes equations, set in a bounded
domain with Dirichlet boundary conditions. The boundaries of the solids and the
domain have H\"older regularity $C^{1, \alpha}$, $0 < \alpha \le 1$. First, we
show the existence and uniqueness of strong solutions up to collision. A key
ingredient is a BMO bound on the velocity gradient, which substitutes to the
standard $H^2$ estimate for smoother domains. Then, we study the asymptotic
behaviour of one $C^{1, \alpha}$ body falling over a flat surface. We show that
collision is possible in finite time if and only if $\alpha < 1/2$.
