Aquatic microorganisms are tiny living organisms that thrive in water environments, including oceans, rivers, and lakes. They include bacteria, protozoa, algae, and viruses, playing essential roles in aquatic ecosystems. These microorganisms contribute to nutrient cycling, help decompose organic matter, and serve as a food source for larger organisms. Many aquatic microorganisms, such as phytoplankton, are crucial for photosynthesis, producing oxygen and absorbing carbon dioxide. Others, like zooplankton, feed on phytoplankton and are vital in the food web. Understanding these microorganisms is important for maintaining healthy aquatic ecosystems and addressing environmental issues like water pollution.