DC's most famous monuments being slowly covered in black slime...
Slimed! Gross 'black slime' creeps over Washington DC's most famous monuments - and no one knows how to get rid of it
- Black slime, otherwise known as biofilm, has been creeping over the National Mall monuments and other iconic areas for a decade
- The biofilm really only needs nutrients and a surface to grow
- The National Parks Service has hired scientists from all over the world to find a solution