Like a slick, gray torpedo, a dolphin breaks the water's surface and leaps into a graceful arc. Its shiny skin glistens in the sunlight, just before it dives deeply again. Marine and river dolphins are highly social mammals that live in groups called schools in oceans and rivers. While many people are fascinated with dolphins, humans also have caused them harm. Fishing practices once decreased the number of marine dolphins. River dolphins are greatly affected by the pollution created by humans. Yet many people are working to protect dolphins and their natural habitats. Learn more in this edition of Nature Watch. Carolrhoda's acclaimed Nature Watch series explores the life cycle of animals and plants through splendid full-color photographs and clear text. Includes glossary, index, and diagrams. Supports the national science education standards Unifying Concepts and Processes: Systems, Order, and Organization; Unifying Concepts and Processes: Form and Function; Life Science; and Science in Personal and Social Perspectives as outlined by the National Academics of Science and endorsed by the National Science Teachers Association.