What is fresh water lens?

Answer 1

In hydrology, a lens is a convex layer of freshwater, floating on top of a denser layer of saltwater. Freshwater lenses occur when rainwater seeps through the surface and gathers over a layer of seawater which is no lower than 5 feet below sealevel. Freshwater lenses are often found on small coral islands and atolls, due to the fact that they are situated at sea level and the surface is quite permeable to rainwater. On islands such as these, freshwater lenses may be the only source of potable water.