A concrete block at the bottom of Port Douglas channel that damaged two Quicksilver reef tour boats has been removed, but mystery over its origin remains.

The concrete cube, measuring exactly one metre on a side, has apparently been submerged for some time and is encrusted with barnacles and other marine life.

Marine Safety Queensland removed the block on Friday after two tour boats operated by Quicksilver struck the block on July 13, taking them out of operation for several days each. 

A Transport and Main Roads spokesperson said apppears the block had been in the water for several years and that vessels might have passed over it in the past but only struck it recently due to spring low tides.

The two tour boats, Poseidon and Wavedancer, struck the block at about 4:30pm, about an hour after the minimum low tides for the day on July 13.

Where do you think the block might have come from?

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