Aquatic plants, especially those that live in the oceans, are among the most important elements of life on Earth. These plants, ranging from microscopic algae to large plants such as seagrasses, play a fundamental role in oxygen production, carbon dioxide absorption, ecological balance, and the food chain of marine animals. They perform a significant part of global photosynthesis and are effective in combating the phenomenon of global warming. The importance of these plants is not limited to their biological function, but they are also known as shelter, food source, and even natural pharmacists. Some algae have medicinal compounds and are also used in the pharmaceutical and food industries. This article was prepared with the aim of familiarizing teenagers with the key role of these plants, their ways of life, and their relationship with marine organisms, and attempts to introduce the underwater world from the perspective of plants in a simple and scientific language. The threats these plants face, such as pollution, rising water temperatures, and destruction of seabeds, are also examined so that teenagers, as the next generation, can take an informed view of protecting the marine environment.