Since it says laguna and not río, I assume you don't mean the River Styx.

I have foundsome refs for Lake Styx, but I think the above is more common.

"The Stygian Lake with the ireful sinners fighting" -- by William Blake.

http://www.mtholyoke.edu/lits/library/arch/col/rare/rarebook...

From hence Virgil takes occasion to show how vail the goods that are committed into the charge of Fortune; and this moves our author to inquire what being that Fortune is, of whom he speaks; hich question being resolved, they go down into the fifth circle, where they find the wrathful and gloomy tormented in the "Stygian Lake".

Without whose aid you durst not undertake
This frightful passage o'er the Stygian lake, (1st ref)


LAKE STYX

The fourth river goes out on the opposite side, and falls first of all into a wild and savage region, which is all of a dark-blue color, like lapis lazuli; and this is that river which is called the Stygion River, and falls into and forms the Lake Styx, and after falling into the lake and receiving strange powers in the waters, passes under the earth, winding round in the opposite direction to Pyriphlegethon, and meeting in the Akherusian Lake from the opposite side.
http://www.theoi.com/Okeanos/Styx.htm

Tartarus has rivers for various purposes and a lake called Lake Styx. Souls who are not especially good or bad are purified for a year and released. Very bad, "incurable" ones remain forever. Those who are not so bad can ask those they wronged for forgiveness and, if it is granted, be released.
http://www.bibleexplained.com/Gospels/Luke/Lu16b.html

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Note added at 1 hr 23 mins (2003-11-01 22:27:16 GMT)
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Tartarus. The fourth river (Cocytus) is that which is called by the poets the Stygian river, and falls into, and forms the lake Styx, receiving strange powers in the waters. This river, too, falls into Tartarus.
http://plato.evansville.edu/public/phaedo.htm

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Note added at 1 hr 25 mins (2003-11-01 22:29:14 GMT)
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This is the ref for: From hence Virgil takes occasion to show how ...

http://www.worldwideschool.org/library/books/lit/poetry/TheD...

Se encuentra esta equivalencia (Laguna Estigia = The Styx) en varias páginas especializadas:

Cocytus, i, m: Cocito, río del Averno.

Styx, igis y -igos, f: la laguna Estigia...

vereda.saber.ula.ve/mun_clas/Arslatina/poetarum.doc


Numancia_2
... Carón* del otro lado, Caronte, personaje encargado de llevar las almas de los muertos en barca al otro lado de la Laguna Estigia (STYX) y el río Aqueronte. ...

www.ups.edu/faculty/velez/Span_480/Numancia_2.html


... La barca. de Aqueronte (The Boat of Charon),1887, and Laguna estigia
(THE STYX), 1887, for which he received a gold. medal. La barca ...
www.geringerart.com/p12.html

Aquiles
... su madre decidió ungirlo de ambrosía y sumergirlo en la Laguna Estigia agarrándolo por ... to anoint it of ambrosia and to submerge it in THE STYX taking hold ...

www.aquiles.org/

[PDF] Anexo I Ilustraciones

Page 9. • 217 • I LUSTRACIONES Foto 12: «Paso de la Laguna Estigia». El pintor flamenco del siglo XV, Joachin Patinir fue uno de ... "Crossing THE STYX”. ...
www.medwet.org/online/culture/cult3.pdf