The man jumped into the city of San Diego-owned reservoir north of Alpine to cool off about 4:20 p.m. Sunday, and could not keep up with the boat as it drifted away, said San Diego lifeguard Lt. Andy Lerum.Rescuers began their search Sunday, Lerum said.The man's body was found shortly after 3 p.m. by rescue divers, said Lt. Paul Robbins of the San Diego County Sheriff's Department.Maurice Luque of the San Diego Fire-Rescue Department said the man's body was found not far from where the boat had been.Luque said the man was discovered at the bottom of the lake.The man's name has not been released by authorities. His family in Denmark has been notified.Coworkers identified him to 10News as 51-year-old Milt Eisen, who was the general sales manager at the KIA dealership in El Cajon. "Everyone is struggling," said Christopher George, the general manager at the dealership. "We were close you become like family after a while." George told 10News the two had been friends and colleagues for more than a decade. He said they last met on Saturday for coffee. He said Eisen's longtime girlfriend Imelda Salud is also employed at the dealership and that Salud and everyone else at the dealership is having a difficult time with the news."[She is] a mess devastated," said George. George said Eisen was a former body builder and an expert swimmer. He believes something went terribly wrong. "We were thinking he wasn't capable swimming, that something happened and he just was not capable," George said. On Tuesday as the news spread, employees were seen wearing a red and black ribbon in honor of their coworker. "We had grief counselors in today," said George. "It's just an odd feeling." He said he plans to honor his friend in the best way he knows how. "You know, chin up and keep going. We don't give up was his motto. He'd say that," said George.