Lagoon Salinity: It Depends—Both Saltwater & Freshwater Exist

Lagoon = Isolated Water Body, Not Salinity Class

A lagoon is a shallow body of water separated from a larger water body by a barrier. Salinity varies by origin and connection.

Saltwater Lagoons

• Barrier: Sandbar, barrier island, coral reef
• Connection: Tidal inlets allow seawater exchange
• Examples: Venice Lagoon, Laguna Madre (TX/MX), Great South Bay (NY), Chilika Lake (India)
• Salinity: Near-marine to hypersaline (evaporation > input)

Freshwater Lagoons

• Barrier: Sand spit, dune ridge, alluvial deposit
• Source: Rivers, streams, groundwater, precipitation
• Examples: Lake Pontchartrain (brackish/fresh), Florida's coastal dune lakes, Oxbow lakes
• Salinity: <0.5 ppt

Brackish/Variable Lagoons

Most common. Seasonal shifts: rainy = fresh; dry = saline. Estuarine lagoons (e.g., Indian River Lagoon, FL) have complex gradients.

Ecological Significance

Nurseries for fish/shrimp, bird habitat, nutrient filters, storm buffers. Salinity regime dictates species composition.