From the Wikipedia page  which has a number of links.
Transitus Fluvii ("passing through the river" in Latin), or Passage Du Fleuve (in French), is an occult alphabet consisting of 22 characters described by Heinrich Cornelius Agrippa in his Third Book of Occult Philosophy (Cologne, 1533, but written around 1510). It is derived from the Hebrew alphabet, and is similar to the Celestial Alphabet and Malachim. The name may refer to the crossing of the Euphrates by the Jews on their return from Babylon to rebuild the Temple.
This alphabet can also be found in Abraham de Balmis Peculium Abrae. Grammatica hebraea una cum latino, Venetiis, 1523, sig. B6v. Also in Geoffroy Tory, Champ Fleury, Paris 1529, f. 76v ubi tamen: “Lettres Chaldaiques,” and Giovanni Agostino Panteo's Voarchadumia contra alchimiam, Venice, 1530, pp. 545–46. Pantheus claims that, while the Hebrew alphabet was entrusted to Moses and Enochian language to Enoch, the Transitus Fluvii was entrusted to Abraham.
See also Malachim