The soil under the marshes and lakes is sandy. Except for lakes and channels, most
of it is covered with large areas of marshes developed on floating organic soils
(histosols), formed by semi-degraded plant material, roots and vegetation, locally
called embalsados. The embalsados are usually those that define a semi-dynamic
perimeter of the main lakes and channels (such as Lagunas del Iberá) and not
necessarily the existence of solid ground, except in marginal sectors of the system