Inclement weather and creative differences have prompted filmmakers to stop shooting.

A statement from a HBO network representative to, reads: "For creative reasons, director John Curran and director of photography Rob Hardy will be leaving the production. We will be bringing on a new director, and we plan to resume filming as soon as possible."

Lewis and Clark led the Corps of Discovery Expedition in the early 1800s and became the first men to cross what is now the western portion of the United States, from the Mississippi River to the Pacific coast.

Casey Affleck, who appeared alongside producer Pitt in The Assassination of Jesse James by the Coward Robert Ford, and Matthias Schoenaerts have been cast as the two adventurers in the six-hour series, adapted from Stephen E. Ambrose's book Undaunted Courage.