Half a dozen people were rescued by helicopter, as ranchers were working to get their livestock to higher ground

Record-breaking flooding has forced dozens of people on a South Dakota reservation to evacuate and ranchers were working on Thursday to get their livestock to higher ground while waiting for a river to crest.

High water from the Moreau river is threatening about 50 residences in an eight-mile (12.8km) stretch between White Horse and Thomas in north-central South Dakota, said a Cheyenne River Sioux Tribe spokesman, Remi Bald Eagle. He said about half a dozen people were rescued by helicopter. The tribe has asked others to voluntarily evacuate.

Bald Eagle said no injuries have been reported but some residents are refusing to leave because their cattle are trapped by flooding.

“Everybody is afraid that their livelihoods are going to be swept up by the water, obviously,” Bald Eagle said. “It is really a critical time for the livestock folks because right now their cattle are all calving.”

The reservation has deployed 20,000 sandbags and a Pennington county rescue team is on hand if needed.

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The National Weather Service said the worst appears to be over. The river has been as high as 28ft (8.5m), or 8ft above flood stage. It stood at about 23ft on Thursday morning and is expected to crest at 24ft over the weekend, South Dakota meteorologist Jeff Chapman said.

On the Pine Ridge reservation in southern South Dakota, the Oglala Sioux tribe is transitioning into recovery mode after flooding swamped roads, trapped people in homes and cut off water supplies to thousands.

“A lot of people lost their homes,” said the state representative Peri Pourier, who is executive director of the Pine Ridge Reservation Emergency Relief non-profit. “It’s going to be a big recovery effort – getting the manpower, the materials and resources to help recover.”

Elsewhere, meteorologists in Montana said a spring storm that is bringing rain and snow may lead to additional flooding as the runoff flows into rivers and streams already swollen with snowmelt. And the North Dakota governor, Doug Burgum, declared a statewide flood emergency after touring inundated homes in the western part of the state on Wednesday.

Rain is expected to prolong the flood fight along the swollen Missouri river, creating a second crest east of Kansas City. The river’s first crest is still making its way downstream, but the worst of the flooding is upstream in Missouri’s Holt and Atchison counties, where multiple levees breached.