If you own land that contains freshwater lakes and streams -- but you're near the boundary where freshwater turns to saltwater at the coast -- the last thing you need is saltwater encroaching on freshwater areas. But that's exactly what can happen if drought is affecting the amount of freshwater on your land, and if saltwater starts flowing into your lakes and streams, the life in those lakes and streams can quickly die. Erecting a barrier to keep saltwater out is essential.
While some fish can live in both fresh- and saltwater -- salmon comes to mind -- many fish have to stay in only one type of water. If they are exposed to the other type of water, they die due to excess or lack of salt. The change in the salinity of the water causes their bodies to go out of whack through osmosis, with NaCl (sodium) ions rushing in or out of their bodies. A freshwater fish swimming in saltwater will find the water in its body being sucked out and replaced with saltwater, for lack of a better term, and the fish can die of dehydration. In fact, even dual-water, or euryhaline, fish have to adjust to different water types as they transition between oceanic environments and freshwater streams.
Fish bodies are designed to remove excess salt or water. Scientific American notes that the kidneys and gills of marine fish have special features that help rid the fish of extra salt -- but freshwater fish don't have these. Conversely, freshwater fish bodies have ways to grab onto salt in water because a minimum level of sodium is necessary for life. Increase the salinity of a freshwater lake, for example, and the freshwater fish will not be able to clear themselves of the excess salt.
Out of Balance
This becomes a real problem in droughts. Normally, freshwater lakes and rivers stay fresh because their flow of water toward the ocean is stronger than the tidal forces that can bring saltwater inland. But if there's a drought and the flow of freshwater is much lower, then saltwater can begin to rush in.
States are already taking this threat seriously; California for example, started building an emergency barrier in May 2015 in the Sacramento-San Joaquin Delta. Fish are so sensitive to salinity levels that you can't risk any saltwater getting into a normally freshwater area.
And it's not just fish at stake. Salt also causes plants to dehydrate, much like sprinkling salt over vegetables in your kitchen will cause the vegetables to secrete water. Pickled lily bulbs might be a delicacy on the dinner table, but you don't want them in your fish pond.
If your area is under a drought warning and you see water flowing the wrong way, contact a marine construction company (such as Abbott's Construction Services Inc.) immediately. Have them inspect the land to find all the places in which seawater might be starting to flow inland. They can erect barriers, both temporary and permanent, to protect your freshwater holdings.