A cross-border Ebro tributary on the Burgos-Álava boundary, joining the Ebro near Bergüenda. The Omecillo is karst-influenced trout water — limestone clarity, steady flows, characteristic Álava-Burgos pool-and-riffle structure. The gauge sits in Álava but the river is mostly Burgos. Wild brown trout. Best fished from May through July; the middle reaches around Quintana-Martín Galíndez hold the most accessible water.
- Limestone