Rashi: In the water. Radak - it will be a paved path, as if it was a path for a long time.

Radak (11): Many of them perished in Galus.

Radak: Just like there was a path in the Yam Suf, there will be a path in their Pras river.

Malbim: There will be paths in the seas and rivers for the exiles to pass to Eretz Yisrael, just like there were in the Yam Suf and Yarden.