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
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(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