WASHINGTON (AP) – The National Park Service is celebrating its 100th anniversary, but the system is facing a backlog worth billions of dollars.

Projects range from replacing water works at the Grand Canyon to making sure the Jefferson Memorial doesn’t sink into the Tidal Basin.

The bill for deferred work is nearly $12 billion nationwide – a $440 million increase from last year.

President Barack Obama has proposed spending $900 million over three years to reduce the backlog, with another $300 million targeted for restoration projects.

Park Service Director Jonathan Jarvis says he hopes to chip away at the backlog so parks eventually have enough resources to keep pace.

He said there is “a lot yet to do, but … everything is moving in the right direction.”