Dissolved Oxygen (DO) refers to the amount of oxygen that is present in water. It is essential for the survival of aquatic life, including fish, invertebrates, and microorganisms. DO levels can vary based on factors such as temperature, pressure, and the presence of organic matter. Higher temperatures generally lead to lower DO levels, while cooler waters can hold more oxygen. Measuring dissolved oxygen is crucial for assessing water quality in ecosystems like rivers, lakes, and oceans. Low DO levels can indicate pollution or excessive nutrient runoff, which can harm aquatic organisms. Maintaining adequate DO levels is vital for healthy aquatic environments and biodiversity.