Evidence of ‘feminization’ of male fish in the estuaries of Gernika, Arriluze, Santurtzi, Plentzia, Ondarroa, Deba and Pasaia has been discovered. The first cases — 2007-2008 — were detected in Urdaibai, and the most recent data confirm that they are also taking place in other estuaries. Pollutants acting as estrogens are responsible for this phenomenon which, among other changes, is causing ovocytes to appear in male fish.