Quasi gran mar fremendo il quarto ondeggia
Ne l'ampio vaso e 'n su la molle arena,
E scopre la squamosa horrida greggia
E, come isola in mezzo, orca o balena,
E 'l corallo e la perla; e quel rosseggia,
Questa è nel suo candor tutta serena;
E l'onda vaga co 'l suo moto alterno
Somiglia de la luna il corso eterno.
Like a wide sea the fourth river shakes
In its wide bed, on the soft sand,
Showing rugged-skinned, scaly herds
And island-like, there, an orc or whale,
And coral and pearl: the former red,
The latter shines clear in its whiteness.
And with alternating motions the waves
Recall the moon's eternal course.
If our hypothesis is true, the fourth river (out of five) in Torquato Tasso's "Metaphysics of Water" represents -- water proper. This wonderful description draws on the text of Genesis while romanticizing it, as Tasso was doing in those same years working on his long poem Il Mondo Creato; which in its turn may have been inspired John Milton for the central section of his Paradise Lost, though we don't know if the English poet had the opportunity to read Gerusalemme Conquistata as he had with the Liberata. We will even forgive Tasso for going so Baroque as to use a river as a symbol of the sea.
A minor detail: the word horrida in line 3 does not imply "horrible," etc., but echoes the original Latin meaning of it, here rendered as "rugged-skinned."