The Marine Corps issued a press release on the incident occurring during the joint landing combat drill (July 3, 2020)

A small rubber boat capsized in waters off Taoziyuan Beach in the morning of July 3^rd due to swift change of nautical weather conditions, when the Marine Corps was conducting its joint landing combat drill, leaving 3 hospitalized with critical drowning-related conditions.
A special task force has been formed by the Navy Command Headquarters and the Marine Corps for investigation.