Aquatic life under our oceans, lakes, rivers, and streams is amazing! From microscopic zooplankton to the largest animal on earth, the blue whale, underwater life comes in all possible shapes and sizes. With 71% of the earth being covered with water, it is no wonder we are so fascinated with what lies beneath the surface. In fact, scientists estimate that there are nearly 1 million different species of aquatic animals. Freshwater ecosystems are home mainly to fish, invertebrates, and reptiles, whereas the ocean contains a wide array of marine life including fish, mollusks, crustaceans, reptiles, sharks, and marine mammals like whales, dolphins, seals, and manatees.