People in the U.S. state of North Dakota are angry because an oil company is building a multibillion-dollar pipeline under a lake near their land. The Sioux people have lived on the land for thousands of years. The Sioux are Native Americans. They have been joined by many protestors. They are all trying to stop the $3.8 billion pipeline. They say it will dirty their drinking water. They also say the pipeline will damage sacred Sioux sites. A company from Texas, Energy Transfer Partners, owns the 1,885-km pipeline project. It is almost complete.

The protestors call themselves "water protectors". They have been trying to block the pipeline for months. They were recently joined by U.S. military veterans (retired soldiers, sailors and members of the air force). The veterans built the protestors shelters to keep warm in the freezing winter. There has been violence between the protestors and police. A North Dakota spokesman said some of the protestors were "frightening". However, a Coast Guard veteran said: "We will be unarmed, completely prepared for peaceful protest. We don't even like the word 'protest'. We're there to help."