"Salinity is how salty the water is. The ocean is very salty — about 35 parts per thousand. Fresh water has almost no salt. The lagoon is in between — it's an estuary, where fresh and salt water mix. That mixing is what makes the lagoon so special."
What Is Salinity?
Salinity is the measure of dissolved salt in water, expressed in parts per thousand (ppt) or practical salinity units (PSU). The open ocean has a salinity of about 35 ppt. Fresh water (rivers, lakes, rain) has a salinity near 0 ppt. The Indian River Lagoon is an estuary — a place where fresh water from rivers, creeks, and canals meets salt water from the ocean through inlets. The lagoon's salinity varies dramatically: near the inlets (Sebastian, Fort Pierce, Canaveral), salinity is close to ocean levels (30-35 ppt). Far from inlets, especially in the northern lagoon and Mosquito Lagoon, salinity may be much lower (10-20 ppt). After heavy rains, freshwater runoff can drop salinity rapidly. During droughts, salinity rises. This variation is one of the defining features of the lagoon and affects which species can live where.
