The document discusses several river organisms - otters, kingfishers, fish, and frogs. Otters are mammals in the weasel family that are well-suited to water, with male otters called dogs. Kingfishers are expert fishers known for their blue and orange feathers that dive underwater to catch minnows. Fish come in a wide range of sizes and are the organisms most adapted to aquatic life. Frogs are amphibians with smooth skin that lay eggs in jelly, and some have bright colors to warn of poison.