COASTAL DUNE LAKES

Coastal Dune Lakes FAQs

What is a coastal dune lake? Coastal dune lakes are found within about two miles of the coast. They’re typically shallow and irregularly shaped. They are usually permanent water bodies, but their water levels fluctuate substantially since they create transitory interchanges with the Gulf of Mexico. The lake-water is composed of both fresh and saltwater that comes from tributaries, groundwater seepage (from uplands and from the Gulf), rainfall, exchange with the Gulf, and coastal storm surges. The lake-water is generally colored (e.g., tea or black colored) due to the dissolved organic matter it contains. This is a natural phenomenon, and it’s nothing to be worried about! While these lakes are exposed to normal weather conditions just like any lake, Florida’s coastal dune lakes are also tremendously impacted by hurricane activity (i.e., storm frequency, strength, and duration).   For more detailed technical definitions of a coastal dune lake written by scientists, please click on the links below: Excerpt from A Management Plan for Walton County’s Coastal Dune Lakes (University of Florida’s Florida LAKEWATCH, 2008) Excerpt from the Guide to the Natural Communities of Florida (Florida Natural Areas Inventory and Florida Dept. of Natural Resources, 1990)     What is an outlet/outfall?   One of the most interesting features of Walton County’s coastal dune lakes is their intermittent connection to the Gulf of Mexico. When a coastal dune lake reaches a relatively high water level, it actually breaks through the dune system and the beach sand and empties into the Gulf of Mexico. The channel that is formed between the lake and the Gulf is known as the lake’s outlet or outfall. Depending on tides and weather conditions (particularly wind), saltwater from the Gulf may enter the lake, along with saltwater plants and animals. The drainage of the lake and potential exchange with the Gulf continues until equilibrium is reached and the opening closes.   Are all of Walton County’s coastal dune lakes the same?   Each of Walton County’s coastal dune lakes has its own personality, based on the combination of its size, watershed features, surrounding land uses, and outlet characteristics. Outlet openings vary greatly in length, frequency and duration. They are driven by each lake’s critical high water level as well as prevailing climatic conditions (e.g., droughts and rain).  As a result, some of the dune lakes can be completely freshwater, some brackish, and some salty, with varying degrees of salinity occurring between different lake stages. The changing condition of water chemistry in the coastal dune lakes makes them dynamic, biologically diverse ecosystems.   Where do coastal dune lakes exist?   Coastal dune lakes are reportedly found in limited number throughout the world along the coasts of New Zealand, Australia, Madagascar, and in the United States along the coasts of Oregon, South Carolina, and Northwest Florida.   How important are the coastal dune lakes?   According to the Florida Natural Areas Inventory, Walton County’s coastal dune lakes are imperiled globally because of rarity and critically imperiled in the state of Florida because of extreme rarity. They are also indispensable to our coastline as wetland systems that filter and store water, provide habitat for a wide variety of unique flora and fauna, and exist as a natural estuarine transition between the Gulf and upland areas.