Lake Pontchartrain is home to a surprisingly diverse mix of freshwater and saltwater species. Covering 630 square miles just north of New Orleans, this shallow brackish lagoon has salinity levels that range from about 1.2 parts per thousand on its western side to 5.4 parts per thousand in the east, creating conditions where freshwater fish, marine fish, crabs, alligators, and even occasional sharks coexist in the same body of water.
A Brackish Mix of Freshwater and Saltwater Fish
The lake’s in-between salinity supports an unusually wide range of fish. On the freshwater side, you’ll find largemouth bass, bluegill, channel catfish, blue catfish, black crappie, white crappie, redear sunfish, and freshwater drum. These species are most common along the western shore and near river inflows where the water is less salty.
The saltwater fish are what draw most anglers. Spotted seatrout (speckled trout) and red drum (redfish) are the two most popular game fish, both present year-round. Southern flounder, black drum, Atlantic croaker, spot, striped mullet, sheepshead, and Spanish mackerel also move through the lake. Bay anchovies and Gulf menhaden are among the most abundant small fish, forming the base of the food chain that supports everything above them. In total, U.S. Geological Survey records document dozens of fish species across the lake basin, with the exact mix shifting seasonally as salinity fluctuates by as much as 8 parts per thousand over the course of a year.
Blue Crabs and Shellfish
Blue crabs are one of the lake’s most economically important residents. Louisiana’s commercial blue crab fishery has consistently landed more than 40 million pounds per year since 1997, with some of the richest crabbing grounds found in and around the Pontchartrain basin. In 2024, the statewide harvest was worth roughly $72 million. Recreational crabbers regularly pull traps from the lake’s shallow waters, where both adult and juvenile crabs thrive in the brackish conditions. The minimum legal harvest size is five inches across the shell.
Bull Sharks and Alligator Gar
Bull sharks were once common enough in Lake Pontchartrain to turn up in beach seines along the shore. They tolerate low-salinity water easily and historically used the lake as feeding and nursery habitat. But their numbers have collapsed. Research comparing fish surveys from the 1950s to the early 2000s found that bull shark abundance in the lake dropped by roughly 99%, making them functionally absent from areas where they were once regularly caught. Environmental degradation and changes in the broader fish community are likely factors.
Alligator gar, the other apex predator in the lake, followed a similar trajectory. These massive freshwater fish, which can grow over six feet long, were rarely captured in surveys after the 1970s. Both species still exist in Louisiana waters, but neither plays the ecological role in Lake Pontchartrain that it once did.
Alligators Along the Margins
American alligators live in and around Lake Pontchartrain, though they favor the marshy edges, bayous, and canals feeding into the lake rather than the open water. Louisiana is home to more than a million wild alligators, and the state’s coastal marshes, which surround much of the Pontchartrain basin, account for more than 3 million acres of available habitat. Mature males tend to stay in deeper water, while nesting females and juveniles stick to shallow marsh areas with dense vegetation. Encounters with alligators near boat launches, fishing piers, and shoreline neighborhoods are not unusual.
Gulf Sturgeon
Lake Pontchartrain sits at the western edge of the Gulf sturgeon’s range. This ancient, armored fish, a subspecies of Atlantic sturgeon, is listed as threatened under the Endangered Species Act. Gulf sturgeon hatch in freshwater rivers, spend time in the open Gulf as juveniles, then return to rivers to spawn as adults. They move into coastal rivers in early spring when water temperatures reach 59 to 68 degrees, depositing eggs on rocky river bottoms. Seven spawning populations have been identified across the Gulf Coast, including one in the Pearl River system that feeds into Lake Pontchartrain. Their numbers declined sharply due to overfishing, dam construction, and habitat loss before federal protections were established in 1991.
Manatees as Seasonal Visitors
West Indian manatees are not permanent residents, but they show up in the Lake Pontchartrain basin more often than most people expect. During warmer months, individuals disperse westward from Florida’s population and occasionally reach Louisiana. Between 1929 and 1994, only 19 manatee sightings were reported in the entire state. That number jumped to 58 sightings between 1995 and 2001 alone, with many concentrated in and around the Pontchartrain basin. Manatees cannot tolerate water below about 68°F for long, so they leave before winter sets in. Those that fail to migrate can lose their appetite and starve in the cold.
Birds Above and Around the Lake
The lake and its surrounding marshes support a wide variety of resident and migratory birds. Brown pelicans, Louisiana’s state bird, are a common sight, along with laughing gulls, royal terns, Caspian terns, Forster’s terns, and black skimmers. Least terns and gull-billed terns nest on flat rooftops near the lake in New Orleans, an unusual adaptation to urban shoreline development.
The freshwater marshes feeding into the lake host pied-billed grebes, king rails, purple gallinules, common moorhens, least bitterns, and mottled ducks. Red-winged blackbirds and boat-tailed grackles nest in both fresh and salt marsh. As salinity increases closer to the coast, the bird community shifts to salt-adapted species like clapper rails and seaside sparrows. Larger seabird colonies, including American oystercatchers and reddish egrets, nest primarily on barrier islands farther offshore where raccoons and other ground predators are absent.
Invasive Species in the Lake
Giant salvinia, a floating aquatic fern, is one of the most destructive invasive plants in the Pontchartrain basin. It reproduces rapidly, forming dense mats on the water surface that block sunlight and prevent atmospheric oxygen from reaching the water below. As the mats decompose, they consume dissolved oxygen on the bottom, suffocating fish and other aquatic life and displacing native plants. Nutria, large South American rodents that have been established in Louisiana for decades, cause extensive damage to the marsh vegetation surrounding the lake, accelerating coastal erosion in habitats that many of the lake’s species depend on for breeding and shelter.