Read Exodus 15:23 Using Other Translations
And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah.
When they came to Marah, they could not drink the water of Marah because it was bitter; therefore it was named Marah.
When they came to the oasis of Marah, the water was too bitter to drink. So they called the place Marah (which means “bitter”).