Crayfish Festival Activity · Herrera de Pisuerga, La Ojeda, Palencia Image of Herrera de Pisuerga, not of the place itself. Every August Herrera devotes its main festival days to the native river crayfish that made its waters famous, a celebration that is maintained despite the collapse of the populations from crayfish plague. Photo: Valdavia (CC BY-SA 3.0) What to see and do in Herrera de Pisuerga