Keywords: fish swimming, vortices, krill, fins Abstract: We consider two problems related to the propulsion of flexible surfaces in vortex wakes. First, we present a simple model of a trout swimming in a cylinder wake, which saves energy by slaloming through a vortex street. We find analytic solutions and compare with previous experiments and numerics. Second, we study ``inverted drafting'' in flags, in which the drag force on one flag is increased by excitation from the wake of another. The types of drafting and dynamics (synchronization and erratic flapping) depend on the separation distance between the flags. We may also discuss recent work on krill swimming and an optimal design for fish fins.