Toilets, construction debris and a boat engine were among the items found during two major sea clean-ups carried out this year.
The Malta Airport Foundation even brought in a crane to help collect 3.6 tonnes of waste from Senglea and Sliema's Tigne.
Divers and land volunteers also helped recover glass bottles, car tyres and broken boat parts from the sea. The crane was used at Tigne to help lift steel construction material.
"Given that we operate in the tourism sector, we consider it our duty to do our bit to safeguard the Maltese Islands' underwater world, which is a very attractive part of Malta's tourism offering," said Malta Airport foundation Chairman Josef Formosa Gauci.
He said the airport's charity wing worked with two diving clubs, Atlam and Calypso to help identify the underwater spots that were "in dire need of a clean-up due to improperly disposed of waste".
Marine debris injures and kills marine life, interferes with navigation safety, and poses a threat to human health.
The foundation has been collaborating with the two clubs since 2020 as part of its annual sea clean-up initiative.
In its first year, the operation collected 1.6 tonnes of waste from Birżebuġġia and Wied iż-Żurrieq. Last year some 1.8 tonnes of debris was lifted from Mrasaxlokk and Marsalforn.
It means the operation has lifted a total of seven tonnes of marine waste from the seabed since the start of the initiative.
The foundation has also previously partnered with the eNGO Zibel on the installation of two seabins in Marsaxlokk and Marsascala.