The Lower Otay Reservoir spilled over its dam today for the first time in six years because of Monday’s heavy rainfall, the city of San Diego reported today. The reservoir crested and began to spill into the Otay River Valley, but no downstream danger was anticipated, city spokeswoman Alma Rife said. “The reservoir serves as a terminal reservoir for a significant-sized watershed, imported water aqueducts and a source of local water for the Otay Drinking Water Treatment Plant,” Rife said.