Because marine hydrokinetic (MHK) turbine technologies are still in their infancy, their impacts on the environment remain largely unknown. Although few empirical data exist for MHK technologies, more data are available for other man-made structures. This paper discusses fish, mammal, bird, and benthic organism interactions with MHK devices and other man-made structures that may be analogous to these MHK technologies. In experiments conducted on the Mississippi River Lock and Dam No. 2, the survival of several species of small and large fish that passed through an MHK turbine was 99%. No data on mammal, sea turtle, or bird interactions with MHK turbines were available, but other types of anthropogenic mortality and traumatic injuries to these groups of animals have been well documented. Collisions with ships and fishing gear have greatly impacted most groups of marine mammals. Large whales that inhabit shallow coastal waters and diving birds that use sight to pursue prey underwater are at risk for collision. However, many devices have a positive impact on fish or benthic organism populations because they act as fish aggregation devices or artificial reefs.