The seafloor is not just flat. In fact, it includes many of the landscape features that you see on land: hills, mountains, valleys and even rivers and lakes! Underwater lakes and rivers form on the bottom of the ocean when seawater seeps up from the seafloor, dissolves the salt layer around it, and collects in the resulting depressions. Incredibly, these underwater lakes and rivers have shorelines, surfaces, and even waves! Masses of mussels line the edges of some of these lakes. The mussels have adaptations that allow them to get their nutrients from bacteria that generate energy from chemicals in the water rather than sunlight, since there isn't any. Lakes deep within the ocean and the kinds of life that thrive there are just a few of the fascinating features of the seafloor.