BISMARCK, N.D. (AP) — Leaders of the Mandan, Hidatsa and Arikara Nation in North Dakota sued the federal government Wednesday due to a Department of Interior opinion that sides with the state over valuable mineral rights beneath a portion of a man-made lake on the Missouri River.

The Three Affiliated Tribes’ lawsuit said the Interior Department is attempting to illegally take part of the Fort Berthold Indian reservation ceded to the tribe before statehood. The lawsuit seeks unspecified monetary damages.

At stake is an estimated $100 million in unpaid royalties and future payments certain to come from oil drilling beneath the river, which was dammed by the federal government in the 1950s, flooding more than a tenth of the 1,500-square-mile (3,885-square-kilometer) reservation to create Lake Sakakawea.

The issue of mineral rights ownership beneath the big lake has escalated over the past decade, after oil companies began using an advanced horizontal drill technique to tap oil beneath the waterway.

Three Affiliated Tribes Chairman Mark Fox said in a statement that the federal agency, as trustee of American Indian lands, “violated both its fiduciary duty as the tribe’s trustee and its treaty obligations” in a “false” opinion in May that said the state is the legal owner of submerged lands beneath the river where it flows through the reservation in west-central North Dakota.

The memo by Daniel Jorjani, solicitor for the department, said a review by Historical Research Associates, Inc. shows the state is the legal owner of submerged lands beneath the river. That contradicts a January 2017 memo by former solicitor Hilary Tompkins, the department secretary under Obama and enrolled member of the Navajo Nation.


The state has argued it assumed ownership of the riverbed when North Dakota became a state in 1889, citing a constitutional principle known as the Equal Footing Doctrine. Under that rule, the Three Affiliated Tribes claim “is not dissimilar” to one by the Red Lake Indian Reservation of Minnesota that was rejected by the U.S. Supreme Court, the Interior Department opinion said.

The tribes argue three previous federal opinions dating back to 1936 have confirmed their ownership of the Missouri River riverbed.

The state has since successfully lobbied the Interior Department to put the issue on hold in order to review the “underlying historical record” of ownership of the river. That came after North Dakota Attorney General Wayne Stenehjem, a Republican, wrote a letter to the Interior Department in October 2017 asking that the Obama-era opinion be withdrawn or suspended.

The Three Affiliated Tribes and the state have long been at odds over shared tax revenue on land-locked parts of the reservation, which is in the sweet spot of the oil patch in North Dakota, the No. 2 oil producers behind Texas.

Since 2007, the state and the tribes have shared more than $2 billion in oil tax revenue.