NEW TOWN, N.D. (AP) _ Leaders of North Dakota’s Mandan, Hidatsa and Arikara nations say that while they are thankful for the money that oil has brought the once-impoverished Fort Berthold Indian Reservation, they are concerned about the environmental impact of drilling on their land.

The Three Affiliated Tribes opened their third annual oil and gas conference Tuesday at the 4 Bears Casino in New Town, on the northwestern North Dakota reservation. One of the first speakers to take the stage, stationed next to a banner proclaiming “sovereignty by the barrel,” was Mervin Packineau, a tribal councilman.

“Our economy is really looking good,” he said. “But now it’s time to turn around and start protecting our land, guys.”

In February, the reservation’s oil production accounted for more than a quarter of the state’s daily total, according to the state’s Department of Mineral Resources. Tribal officials say that would put the reservation among the top ten oil producers in the nation.

But the sentiments of some tribe members are far removed from the, “Drill, baby, drill,” mantra printed on T-shirts for sale at gas station convenience stores elsewhere in the oil patch. It reflects what they say is a strong, personal connection to the land and their long history in a place where most residents didn’t arrive until the start of the oil boom, about five years ago.

Recent oil spills and incidents involving the illegal dumping of oil production byproducts have highlighted the environmental risks associated with drilling.

Wayde Schafer, the lone Sierra Club staffer in the state, said Wednesday that public concern over the oil industry’s impact, including its effect on the environment, has grown since the boom began. Schafer has said before that is isn’t easy being green in a red state where even most Democrats encourage industrial development.

In a smaller breakout session away from the main auditorium, Edmund Baker of the Hidatsa tribe, the Three Affiliated Tribes’ environmental director, said the oil industry should be careful with its activity and encouraged greater regulation.

His views, he said, were based on his experience of being “from a place where you actually see it happen. … Sacred sites being leveled _ now there’s an oil pad there. Your identity, your memories of your ancestors, your parents, your grandparents, all of this is an abrupt shock, change.”

The changes to the land and the way of life on the reservation are a trade-off the tribes have had to make to reap the economic benefits of North Dakota’s oil boom, he said.

Packineau said Tuesday that less than a decade ago, the tribe was struggling financially and forced to take out loans from other tribes.

The tribes say they are proud of the environmental clauses of their oil and gas regulations, which require oil wells to be located more than half a mile from bodies of water and promote the use of multiple-well drill pads to reduce the industry’s footprint. But officials also say more needs to be done.

“Every day we hear of a lot of spills happening,” said Fred Fox, vice chairman of the tribes’ executive committee.

Baker, the tribes’ environmental director, said spills on the reservation have resulted in brownfields, places where nothing grows.

While some big oil companies are involved in production on the reservation, they often hire contractors to work their sites.

“A lot of times they believe that they don’t have to follow the rules here on our reservation,” Baker said. “We don’t want to hinder the development, yet we want to make it more environmentally protective for our reservation.”

Baker said he did not support the reservation hosting oil field waste disposal sites, saying it dishonors the ancestors of tribe members.

 “I’m not anti-oil. … I’m anti-irresponsible,” he said.