Complex sentence: The southern river otter can be found in marine, freshwater, and terrestrial habitats, but are mostly found in freshwater lakes and rivers having a significant amount of dense vegetation, especially along the shorelines, which must be present to use as cover.
Split into simpler sentences: The southern river otter can be found in marine, freshwater, and terrestrial habitats, but are mostly found in freshwater lakes and rivers. Having a significant amount of dense vegetation, especially along the shorelines, must be present to use as cover.