Swāt valley, located in the Khyber Pukhtunkhwa (KPK) province of the northern part of Pakistan, was known since the antiquity with the names of Uḍḍyāna (‘the garden’) and Suvāstu (‘the place of fine dwellings’). The Yusufuzai Pashtuns, whose penetration in the valley begun towards the 16th century, little by little replaced the probably autochthon Dardic populations who are actually confined in the northern mountainous part of the district, i.e. the Tehsils of Bahrain and Kalam. This article focuses on hydronymy and presents the first results of the toponymic project of the Swāt valley, held with the support of the Italian archaeological mission, working in Swāt since 1956 and continuing its researches under the direction of Luca Olivieri and the auspices of the ISMEO of Rome. As it is known, hydronymy is one of the most conservative branches of the toponymy: in the Swāt context, nearly all stream names are of Indo-Aryan (Dardic) origin, except names derived from the denomination of the Pashtun villages: this confirms all data provided by the archaeological excavations. This article will also provide some specific etymologies, aimed at showing the frontier position of Swāt at the border between Iranian and Indo-Aryan languages and cultures.