The authors describe a new morel species, Morchella fluvialis, found in riparian forests along rivers in Spain. M. fluvialis is genetically distinct but closely related to M. esculenta. It differs morphologically from M. esculenta in having a longer, more slender stipe often twice as long as the conical pileus, and primary pits that are elongated and stain orange when damaged. The species appears restricted to riparian habitats containing Fraxinus angustifolia, F. excelsior, or Ulmus minor trees in Spain. Due to its habitat specificity, the authors suggest M. fluvialis requires monitoring as a potentially vulnerable species.