How deep - and how long - is the reflecting pool in Washington DC?

The Lincoln Memorial Reflecting Pool - rich with history 100 years after being constructed - is currently undergoing a dramatic transformation ordered by President Donald Trump.

The changes, which will see the reflecting pool turn "American Flag Blue," coincide with Trump's beautification plan ahead of the nation's 250th anniversary.

But not everyone is too happy about the makeover. The Cultural Landscape Foundation sued the U.S. Department of the Interior on Monday, taking issue with changing a "key character-defining feature."

As renovations continue, here is what to know about the history of one of DC's most iconic landmarks.

When was the Lincoln Memorial Reflecting Pool constructed?

Construction on the reflection pool was completed just after the Lincoln Memorial's dedication in 1922, providing the National Mall with one of its most key features.

It was designed by Henry Bacon, who received the commission to design the Lincoln Memorial in 1912.

How long is the Lincoln Memorial Reflecting Pool? How deep is the Lincoln Memorial Reflecting Pool?

The reflecting pool spans from the Lincoln Memorial toward the Washington Monument, encompassing 2,028 feet.

Closer to the Lincoln Memorial, the pool is 160 feet wide. Toward the World War II Memorial ahead of the Washington Monument, it's 175 feet wide.

The National Parks Service says it contains 6.75 million gallons of water. It ranges from 18 inches deep at the edges to 30 inches deep in the middle.

Has the reflecting pool been reconstructed before?

The reflecting pool sunk about a foot after its original construction, as it did not have pilings to support it, according to the Trust for the National Mall.

That caused cracking and leaking, with the pool needing to replenish 30 million gallons of water annually.

So reconstruction on the pool began, and it was completed in 2012. Originally with an asphalt and tile bottom, it was rebuilt with a reinforced concrete basin and modern waterproofing systems designed to prevent leaks and sinking issues.

New sustainable water conservation features in the rebuild included "a new water supply system, with water being drawn from the Tidal Basin... treated with an ozone water filtration system," according to the Trust.