People have affected lakes and river by pollutant dumping, but a less obvious impact is in the human affects on biota. Because freshwater systems are managed intensively, most no longer have their original species. Fisheries managers constantly introduce fish species, from carp in the 1800s to modern-day regular introductions of desirable game species. Use of live bait is responsible for the introduction of many invertebrates and fish. Aquarium trade, with associated dumping.
Boats transport aquatic plants.
Ship ballast caries aquatic organisms around the world.