For the 2019–20 school year, Mariner honored its 50th anniversary by holding a celebration prior to its (football) homecoming game against Mount Vernon High School on October 11. District administrators attended the event along with school alumni and former school employees. However, the school's anniversary was marred by the COVID-19 pandemic; the district temporary closed Mariner on March 2, 2020, due to a student's parent testing positive for COVID-19 before permanently closing all its schools for the rest of the school year on March 12 under the statewide mandate of Governor Jay Inslee.