Parallel
Exodus 15:23
Rahlfs Septuagint (1935) · Berean Standard Bible
ἦλθον δὲ εἰς Μερρα καὶ οὐκ ἠδύναντο πιεῖν ἐκ Μερρας πικρὸν γὰρ ἦν διὰ τοῦτο ἐπωνομάσθη τὸ ὄνομα τοῦ τόπου ἐκείνου πικρία
And when they came to Marah (note: Marah means bitter.), they could not drink the water there because it was bitter. (That is why it was named Marah.)