One of America's most revered memorials has been covered by a microbial film that is proving a monumental headache for officials.

Conservationists are at a loss for how to stop the organisms covering the once gleaming dome of the Jefferson Memorial in Washington DC.

The black biofilm became noticeable less than a decade ago, National Mall and Memorial Parks spokesperson Catherine Dewey told the Washington Post.

She said it had grown "immensely" in recent years.

Image: The biofilm became noticeable less than a decade ago, say officials

One microbiologist told the newspaper she does not know whether the microbes are damaging the surface.


The Park Service is trying out different cleaning solutions to remove the bacteria.

But officials are unsure whether they can even stop the organisms coming back.

The white neoclassical structure was built 73 years ago to honour the nation's third president, the principal author of its Declaration of Independence.