This black wooden box washed up on Boscombe beach on Monday morning.
Coastguards were called to deal with the crate, which is covered in goose barnacles.
Stephen Avery and his neighbour, Fran Clowery, noticed the box on the beach near to Boscombe Pier at around 7.30am.
He said: "We hope that it is a treasure chest. It was quite a surprise. It's just a big box, which is about 3ft by 2ft and around 4ft across.
"We have been told that we can keep whatever's in it if nobody claims it, but we don't know what is in it yet."
After a great deal of speculation from Echo readers about what might be inside, ranging from lost episodes of Doctor Who to Lord Lucan, Elvis and Shergar via Pandora and horror film Se7en, the coastguard rescue team finally revealed the contents.
The team said the box was believed to be part of a pontoon that had broken away, and contained nothing but foam.
The box has now been removed by the council.