Golf ball diver Ralf Oestmann with golf balls that he retrieved from a pond on a golf course in Bremen, Germany, earlier this month.

Mr Oestmann dives for golf balls that have been lost in the course's water hazard.

Afterwards, the golf balls are cleaned, sorted and re-sold.

Every year, thousands of golf balls land up in the water.

Mr Oestmann said he does not do his job for the golfers but for the pond itself. Left too long underwater, the golf balls break down and end up releasing pollutants that can hurt the flora and fauna of the pond.

Mr Oestmann said that he has found more than just golf balls during his work and has recovered items from golf clubs to car batteries and bicycles. Once, he even found a loaded revolver.

The issue of lost golf balls affecting the environment has been known to the German Golf Association for years. In 2005, the group put together the Golf & Nature programme along with the Federal Agency for Nature Conservation, aimed at combining the conditions of the game with the greatest possible protection of nature.