MIAMI SHORES, Fla. — The marine patrol officers and fish and wildlife agents made an onshore visit Thursday to the home of one Nick Harrington, 16, to deliver an ultimatum: Remove the grand piano from Biscayne Bay within 24 hours or face felony charges, a $5,000 fine or, perhaps, worse.

“The officers asked me, ‘Should your mom get arrested? Or should you get arrested?’ ” Nick said. “I said: ‘Arrest me. It’s my piano.’ ”

The mystery that has gripped much of South Florida and head-scratching Web surfers everywhere for the past week — who dumped an old grand piano on a sandbar and why on earth would anyone do that? — has finally been solved.

The teenager had intended to make a “surreal video” of the piano perched atop the sandbar’s highest point, with Miami’s glittering skyline as a backdrop, to impress the college admissions officers at the Cooper Union in Manhattan, where he hopes to study art or music.