Hubelj is a torrential stream that rises from under the steep cliffs of the Trnovo Forest Plateau in the municipality of Ajdovščina. It then flows down the riverbed towards the northern part of the town, where it calms down and feeds into the river Vipava near the village of Dolenje. In the past, Hubelj had several functions: as a water source in close proximity to one of the main road links, it was one of the factors behind the settlement of this area. In the Middle Ages, it became a border river, first between the Gorizia and Vipava dominions and later between the regions of Carniola and Gorizia. It retained this function until the end of World War I. The river was one of the key factors influencing the development and expansion of industry in Ajdovščina. Its water power was first used to power mills, sawmills, and later also the ironworks and the first modern industrial plants. The contribution at hand presents the river Hubelj as a water source and an influence in the emergence and development of several factors in the 19th and early 20th centuries. The focus will be on the industrial activity along the river and its role in the subsequent development of the town in the 19th century. The impact of the Hubelj river border on the administrative, economic, and social life of the people on both sides will be illustrated.