Singapore is a country with a lot of money, but not much coastline or territory. Cambodia, has an excess of coastline and territory, however the country has very little money. Thus, a deal was struck that would benefit both parties: Singapore bought billions of cubic feet of sand from Cambodia.
This way, Singapore would get enough sand to expand their landmass into the sea to build casinos, hotels, and skyscrapers - and Cambodia would get a lot of money.
The operation involves hundreds of massive barges being sent from Cambodia, down the Tatai River, 24/7, 365 days a year - until the operation is complete.
However, the legitimacy of this deal has been questioned. For example - what has the millions of dollars Singapore gave to Cambodia really been spent on, because there is very little economic difference in the country since the deal. Furthermore, dozens of fishing villages, and hotels have suffered greatly as a result of the beaches that have completely disappeared. Nobody knows what the long term impact of this mass sand removal will be.
For more information on this sketchy deal, read the source!