In this paper we deal with some controllability problems for systems of the Navier Stokes and Boussinesq kind with distributed controls supported in small sets. Our main aim is to control N-dimensional systems ( N + 1 scalar unknowns in the case of the Navier - Stokes equations) with N - 1 scalar control functions. In a first step, we present some global Carleman estimates for suitable adjoint problems of linearized Navier - Stokes and Boussinesq systems. In this way, we obtain null controllability properties for these systems. Then, we deduce results concerning the local exact controllability to the trajectories. We also present ( global) null controllability results for some ( truncated) approximations of the Navier - Stokes equations.