Exodus 14:26

14:26 The Lord said to Moses, “Extend your hand toward the sea, so that the waters may flow back on the Egyptians, on their chariots, and on their horsemen!”

Exodus 15:23

15:23 Then they came to Marah, but they were not able to drink the waters of Marah, because they were bitter. (That is why its name was Marah.)