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NBA champion Elden Campbell 's cause of death has been revealed ... with officials telling TMZ Sports the former Laker died due to an accidental drowning.

Florida officials say Campbell -- who was 57 years old -- passed away on December 1. Getty

The news of his tragic death was first announced by his former teammates and professional and college organizations.

The 6'11" center spent 15 years in the NBA -- more than half of that run with the Los Angeles Lakers, who drafted Campbell in the first round in 1990. Getty

He also suited up for the Charlotte/New Orleans Hornets, Seattle SuperSonics, Detroit Pistons, New Jersey Nets and Detroit Pistons ... winning a championship with Motor City in 2004.

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