Simple photonic fiber-based workbenches have been able to emulate well-known nonlinear wave dynamics occurring in deep-or shallow-water conditions. Here, by investigating the nonlinear reshaping of a flattop pulse upon propagation in an anomalous dispersive optical fiber, we observe that typical signatures of focusing dam break flows and Peregrine-like breather events, can locally coexist into spontaneous pattern formations. Experimental measurements are in good agreement with our numerical predictions.