The incident happened around 8:30 a.m. at the Lyons Park pool located at Victory Boulevard and Bay Street in the Tompkinsville section.
Authorities say both victims, who are in their 20s, were rushed to St. Vincent's Hospital in cardiac arrest.
One of the victims was pronounced dead at the hospital. The other is currently in critical condition at Richmond University Medical Center.
The circumstances of the drowning are unknown at this point, but witnesses say they may have been trying to see how long they could hold their breath underwater, possibly as part of a military practice exercise.
At 7 a.m. every weekday, the pool hosts what's called Adult Swim. Lifeguards are always on duty, and swimmers say at least 15 regulars are in the pool each day. This leaves many wondering how something like this could happen in a somewhat crowded pool."Lifeguards were always on duty," swimmer Irv Chasner said. "They would not let you go in the water until exactly 7 o'clock."
The investigation continues.