Guaymas (formally: Heroico Puerto Guaymas de Zaragoza) is a port city and a municipality in the Mexican state of Sonora. It stands on a small bay on the Gulf of California, near the mouth of the Río Yaqui, south of state capital Hermosillo and north of Ciudad Obregón. It serves as the administrative centre for the surrounding municipality of the same name, and for the neighborhood San Carlos Nuevo Guaymas, Sonora. Guaymas is the second-largest port on Mexico's Pacific Coast (after Manzanillo). It is one of the major shrimp producing cities of northern Mexico and was formerly a major oyster producer, although pollution and overfishing have depleted its stocks greatly. Guaymas is located in a semi-arid flat area. The climate is dry and very hot, with an average monthly maximum temperature of 31º C in the months of July and August and an average monthly minimum temperature of 18.0º in the months of January and February. The average annual temperature is 19ºC. In a tradition dating back to 1888, one of Mexico's liveliest carnivals takes place on the waterfront every spring. In June 2007, local mining conglomerate Grupo Mexico announced plans to build a copper smelter and refinery and a 400MW power plant at Guaymas.