If going in a private boat , you must inform the Prefectura that you are leaving , and notify them on your return. If they choose to visit you , and find irregularities , you could be subject to the penalties Steve mentioned above. You also need a marinaro patente to operate a boat . and if not yours , a notario saying the owner says you can use it. You could also be stopped randomly on the river. Locals have been using the river to bring goods into Argentina for years. Smuggling , weather goods or money , is still smuggling.
Therefore much more difficult to Comia your way out of. But as Henry says above......
Relax, make a few trips , or pay the cueva to get it out. Much easier.