Behold, he drinketh up a river, and hasteth not; rather, behold, let a river overflow, he trembleth not ( ἐὰν πλημμύρα γεηται, οὐ μὴ αἰσθηθῇ' LXX). As an amphibious animal, the overflowing of a river has no terrors for the hippopotamus.
But it would have some terrors for an elephant. He trusteth that he can draw up Jordan into his mouth. It is better to translate, he is steadfast (or, confident)' though Jordan swell even to his mouth.
"Jordan" probably stands for any large and strong-flowing river. The conjecture that ירדן is a corruption of יר, which often stands for "the Nile," is ingenious, but unnecessary.