We generate experimentally different types of two-dimensional Bloch waves of a square photonic lattice by employing the phase imprinting technique.We probe the local dispersion of the Bloch modes in the photonic lattice by analyzing the linear diffraction of beams associated with the high-symmetry points of the Brillouin zone, and also distinguish the regimes of normal, anomalous, and anisotropic diffraction through observations of nonlinear self-action effects.