The Indian River Lagoon is long and narrow like a river, but it is really a saltwater lake connected to the ocean at the inlets. Unlike a river, the lagoon has no particular direction of water flow and moves in whatever direction the wind blows. Salinities range from completely fresh in some of the tributaries and canals to up to 35 parts of salt per thousand parts water (ppt) near the ocean inlets (3.5 percent). The concentration of salt in the Lagoon is critical for the plant and animal species that live in it. Wetlands that did not flow to the lagoon have been drained by canals that now bring more then twice the amount of freshwater the lagoon historically received.

The maps to the right show what happened to the salinity in the Vero Beach area after just a few weeks of rainy weather. In July of 2002, for the first time since the MRC volunteer monitoring program began in 1991, we saw salinity numbers in the single digits in the Lagoon itself. The "epicenter" of the lowered salinity was near the Merrill Barber Bridge (SR60) which is a area much influenced by drainage from the Main and North Relief Canals which run from west Vero Beach in arrow straight lines right into the Lagoon. These lowered salinities persisted for some weeks and it is inevitable that the ecology of the Lagoon suffered in this region. Many fish species can tolerate low salinity but often their eggs cannot be fertilized at low levels because as the water becomes fresher it becomes less dense and the eggs cannot float on the surface to be fertilized. Sustained below 15ppt will kill clams and other shellfish outright. Compare this July map with November, 2002. The salinity has recovered to almost ocean-like values. While high salinities are not bad, these wide seasonal variations are becoming more the "norm" than the exception and increases the stress on our diverse and delicate ecosystem.