Kurdish officials said they were making progress in reclaiming the critical structure from Islamic State militants, though face "fierce resistance."
The Mosul dam is located on the Tigris River 30 miles northwest of Mosul, Iraq's second largest city, which has been under IS control since its capture on June 10. The dam was captured Aug. 7.
The United States began an air assault on the IS fighters at the dam Saturday to prevent them from their push toward Kurdish territory and the city of Erbil, which has a U.S. consulate.
Peshmerga spokesman Halgord Hikmat told CNN clashes between Kurdish and IS fighters on the western side of the dam were ongoing.