The arrow clubtail (Stylurus spiniceps) is considered as a discrete species of dragonfly, associated with the St. Lawrence River and its major tributaries. The discovery of populations in the Montérégie and Estrie Regions confirms its presence in the Appalachians natural province in Québec. The absence of records in the lowlands surrounding the island of Montréal and Saint-Pierre lake could indicate a degradation of the aquatic and forest environment in the downstream portion of the Appalachian and Laurentian watersheds. A set of 8 riverine species of Gomphids can serve as biological indicators applied to the hydrographic system of the St. Lawrence.