Understanding Lake Pontchartrain’s Water
Lake Pontchartrain, in southeastern Louisiana, is an estuary covering approximately 630 square miles. An estuary is a partially enclosed coastal body of brackish water where freshwater from rivers and streams mixes with saltwater from the ocean.
This mixing creates an environment where water salinity fluctuates. Brackish water contains between 0.5 and 30 grams of salt per liter, saltier than freshwater but less salty than seawater. Lake Pontchartrain’s fluctuating salinity provides a habitat supporting diverse life adapted to these changing conditions. This fluctuation is influenced by freshwater input and its connection to the Gulf of Mexico.
Hydrological Influences on Salinity
Lake Pontchartrain’s brackish nature and fluctuating salinity are shaped by hydrological inputs and human-made structures. Freshwater enters the lake from numerous northern rivers and bayous. Key contributors include the Tangipahoa, Tchefuncte, Tickfaw, Amite, and Bogue Falaya rivers, as well as Bayou Lacombe and Bayou Chinchuba.
Saltwater intrusion occurs primarily through connections to the Gulf of Mexico. The Rigolets and Chef Menteur Pass are natural waterways linking Lake Pontchartrain to Lake Borgne, which then connects to the Gulf. These passes allow tidal changes and saltwater to enter the eastern parts of the lake, with salinity increasing further east towards Interstate 10.
Human-engineered structures have also influenced the lake’s salinity. The Bonnet Carré Spillway can divert large volumes of Mississippi River floodwaters into Lake Pontchartrain during high river stages. This influx of freshwater can reduce the lake’s salinity, sometimes displacing up to 75% of the saltwater within weeks. Conversely, the now-closed Mississippi River Gulf Outlet (MRGO), a deep-draft shipping channel, historically increased saltwater intrusion. Its closure in 2009 has helped restore more historical salinity gradients in the basin.
Life in Brackish Waters
The brackish environment of Lake Pontchartrain supports diverse plant and animal life. Organisms in this estuary have adapted to tolerate fluctuating salinity, allowing both freshwater and marine species to coexist. The lake’s varied habitats, including shorelines, marshes, and submerged aquatic vegetation, provide shelter and feeding grounds for many creatures.
Common fish species include red drum, speckled trout, blue catfish, and channel catfish. Flounder, sheepshead, and even bull sharks are also present. Crustaceans such as blue crabs and shrimp are abundant, with blue crabs being a staple of Louisiana cuisine. The lake’s marshes and wetlands also serve as important resting and feeding grounds for bird species, including pelicans, egrets, and herons.
Human Connection and Stewardship
Lake Pontchartrain holds cultural and recreational importance for surrounding communities. Historically, Native American tribes, like the Tchefuncte, Choctaw, and Houma, revered the lake, calling it “Okwata” or “wide water,” and utilized its resources for food and transportation. European settlers later recognized its strategic importance for trade and commerce, leading to the establishment of communities like New Orleans along its shores.
Today, the lake remains a popular destination for recreational activities. Fishing is popular, supporting species sought by anglers and hosting several fishing tournaments annually. Boating, sailing, and kayaking are also common. Efforts to manage and protect Lake Pontchartrain’s health are ongoing, including water quality monitoring and conservation initiatives. Organizations work to improve water quality and restore habitats, promoting responsible recreational use and ensuring the lake remains a valuable resource for future generations.