Oxygen levels refer to the concentration of oxygen in the atmosphere or in water. In the air, oxygen makes up about 21% of the total volume, which is essential for the survival of most living organisms. In aquatic environments, oxygen levels can vary significantly, affecting the health of fish and other marine life. Monitoring oxygen levels is crucial for various applications, including environmental science and healthcare. Low oxygen levels can lead to conditions like hypoxia, which can harm both humans and wildlife. Conversely, high levels of oxygen can be beneficial in certain medical treatments, such as hyperbaric oxygen therapy.