It is the Perat, and it is the river Kevar. "Perat," because it is fruitful and multiplies (pareh ve-raveh) until they cross it by boat. "Perat," because it separates and goes on (mafrid) until it runs out and they open it with a hoe. "Kevar," because its waters are light, so much so that its fruits are coarse and do not pass down through a sieve (kevarah).
What the Names Perat and Kevar Reveal About the River
Yalkut Shimoni on Torah 22:1
הוּא פְּרָת, וְהוּא נְהַר כְּבָר, פְּרָת, שֶׁהוּא פָּרֶה וְרָבֶה עַד שֶׁעוֹבְרִין בּוֹ בִּסְפִינָה. פְּרָת, שֶׁהוּא מַפְרִיד וְהוֹלֵךְ עַד שֶׁהוּא כָּלֶה וּפוֹתְחִין אוֹתוֹ בְּמַגְרֵפָה כְּבָר שֶׁמֵּימָיו קַלִּין עַד שֶׁפֵּירוֹתָיו גַסִּין וְאֵינָן יוֹרְדִין בַּכְּבָרָה.