The state lies entirely within the Gulf Coastal Plain region of the United States and is one of the lowest and flattest areas in the country. The surface has an average elevation of about 100 feet (30 m) above sea level. From the north the land slopes gently downward toward the coast. The coastal section is greatly indented with bays and inlets and is dotted by marshes, shallow brackish lakes, and lagoons. Much of southern Louisiana, including the Mississippi Delta south of New Orleans, is extremely low-lying and marshy and is largely uninhabited. Numerous islands and sandbanks lie offshore. The largest island is Marsh Island.
The state's highest elevations are in the northwest, where some of the land is hilly. The state's highest point, Driskill Mountain, reaches 535 feet (163 m) above sea level. The Mississippi and Red River valleys and their floodplains occupy much of the rest of northern and central Louisiana.Louisiana's state tree is the baldcypress.
Louisiana has a variety of water features. The state is crossed by numerous rivers. Bayous (sluggish small streams) wind through the land, especially in the south, where the surface is flattest and lowest. Rivers are often bordered by swamps, marshes, oxbow lakes, and levees.
The principal river is the Mississippi. Flowing southward along the Louisiana-Mississippi state line, it crosses southern Louisiana and empties into the Gulf of Mexico through multiple channels in its delta. Because of levees built along its banks, many of the rivers that once flowed into the Mississippi now follow different courses to the Gulf.
Most of northern Louisiana is drained by the Red River and its tributaries, particularly the Ouachita-Black river system. The Red River once flowed entirely into the Mississippi, but it has been diverted before its junction with the Mississippi and now flows chiefly into the Atchafalaya River and on to the Gulf. In addition to the Atchafalaya, the large rivers of southern Louisiana include the Bayou Lafourche, Bayou Teche, Calcasieu, Pearl, and Sabine.
Lake Pontchartrain, a brackish lake, is the state's largest natural lake; New Orleans is on its southern shore. Toledo Bend Reservoir on the Sabine River, an artificial lake shared by Louisiana and Texas, is the largest freshwater lake.
The climate is subtropical and varies mainly with distance from the Gulf of Mexico. Summers are hot and humid; winters are mild. July temperatures average from 81° to 83° F. (27° to 28° C.) throughout the state; average January temperatures range from 53º F. (12º C.) in the south to 47º F. (8º C.) in the north. Freezing temperatures, snow, and sleet occur infrequently, especially in the extreme south.
Annual precipitation varies from about 46 inches (1,170 mm) in the north to 66 inches (1,680 mm) in the south. Much of the rain is brought by summer thunderstorms. Hurricanes and tornadoes occasionally strike the state.
Louisiana has a striking variety of natural vegetation. About half of the state is forested. Bottomlands, particularly in the Mississippi and Red River valleys, are forested mainly with cypress and various hardwoods, including oak, water tupelo, willow, and cottonwood. Higher, better drained areas in central and northern Louisiana have both hardwoods and pines, mainly loblolly and shortleaf pine. Farther south longleaf and slash pine are more common. A broad prairie region lies just south of the forests in the southwest. Swamps are found in many parts of southern Louisiana, particularly in the Atcha-falaya basin. These areas support bald cypress and such plants as Spanish moss, vines, ferns, and water hyacinth. Along the Gulf coast are saltwater, freshwater, and brackish marshes.
Wildlife is abundant in the numerous marshes and swamps that are still virtually undisturbed by man. Deer, squirrels, nutrias, raccoons, and muskrats are common. Alligators, frogs, and various snakes are found in many areas. A great variety of fish, crustaceans, and birds thrive in Louisiana's wetlands. The state is visited by numerous species of migratory birds, particularly waterfowl and wading birds, such as egrets and other herons.Louisiana's state flower is the magnolia.