Enviros, who have been heartened in recent months by a growing movement in favor of breaching dams, had cause for remorse on Friday when a gigantic new dam was dedicated in the foothills of the San Bernardino Mountains in Southern California. Enviros fear that the $420 million Seven Oaks Dam, erected above the growing sprawl east of Los Angeles, could be used to create a semi-permanent reservoir, destroying wildlife habitat and harming native fish that have evolved to survive in flowing water. The stated goal of the dam project is to lessen the effects of flooding along the 75-mile course of the Santa Ana River, but critics say that if a reservoir is created, as many local water districts desire, the flood-control benefits could be negated. The 550-foot-high structure, nine years in the making, is the 12th highest dam in the nation.