Complex sentence: Naturally, the operation of military forces in lakes and rivers is not limited to landlocked countries--many states maintain such forces (e.g. Russia's Caspian Flotilla) in addition to their seagoing navy.
Split into simpler sentences: Naturally, the operation of military forces in lakes and rivers is not limited to landlocked countries. Many states maintain such forces (e.g., Russia's Caspian Flotilla) in addition to their seagoing navy.