Passage 1.4.3
ἔνθα δὴ πλείστου παρέσχοντο αὑτοὺς Ἀθηναῖοι τοῖς Ἕλλησιν ἀξίους, ἀμφοτέρωθεν ὡς ἐκυκλώθησαν ἀμυνόμενοι τοὺς βαρβάρους· οἱ δέ σφισιν ἐπὶ τῶν νεῶν μάλιστα ἐταλαιπώρουν ἅτε τοῦ κόλπου τοῦ Λαμιακοῦ τέλματος πρὸς ταῖς Θερμοπύλαις ὄντος· αἴτιον δὲ ἐμοὶ δοκεῖν τὸ ὕδωρ ταύτῃ τὸ θερμὸν ἐκρέον ἐς τὴν θάλασσαν. μείζονα οὖν εἶχον οὗτοι πόνον· ἀναλαβόντες γὰρ ἐπὶ τὰ καταστρώματα τοὺς Ἕλληνας ναυσὶν ὑπό τε ὅπλων βαρείαις καὶ ἀνδρῶν ἐβιάζοντο κατὰ τοῦ πηλοῦ πλεῖν.
Here indeed the Athenians showed themselves most worthy among the Greeks, for they defended themselves bravely against the barbarians who surrounded them from both sides. The barbarians especially suffered hardship on their ships, since the bay near Thermopylae, belonging to the Lamian Gulf, is swampy. It seems to me the cause of this is the warm water which flows into the sea at this place. Thus, the barbarians endured greater hardships; for having taken the Greeks onto their decks, they were compelled to sail through mud, their ships heavily laden with armor and troops.