(CNN) Protesters have tried to stop the construction of the Dakota Access Pipeline since late last summer. They've voiced environmental concerns. They've performed sacred rituals. They've stood in solidarity with a Native American group seeking to be heard.
On Sunday night, 400 protesters clashed with police, leading to the hospitalization of more than two dozen.
One protester, a 21-year-old New York resident named Sophia Wilansky, nearly lost her arm after an explosion. How did it happen? Both sides have blamed each since the weekend clashes.
The proposed Dakota Access Pipeline, which is set to cost $3.7 billion, would start in North Dakota, stretch across parts of South Dakota and Iowa and end in southern Illinois. If completed, the pipeline would allow crude oil to be transported to oil refineries along the Eastern Seaboard.
Wilansky was among the protesters Sunday who rallied in solidarity with the Standing Rock Sioux Tribe. Members of the tribe, whose reservation is near the project's path, believe the pipeline would affect its supply of drinking water and place downstream communities at risk of contamination from potential oil spills. The US Army Corps of Engineers granted the project final permits in July -- to the dismay of environmentalists and tribe members.
Michael Knudsen, medical logistics coordinator for the Standing Rock Medic and Healer Council, told CNN that demonstrators on Sunday had attempted to pull a truck off of the Backwater Bridge to clear a roadblock that "prevented people from being evacuated in an emergency."
Knudsen said he saw police unleash water cannons on protesters even though temperatures were below freezing. They also shot rubber bullets and tear gas toward the crowd.
"It was horrific," one protester told CNN. "It was a horrific scene."
Frightening explosion, fears of amputation
As the protest stretched into Monday morning, police started to fire concussion grenades at protesters, Knudsen said.
Wilansky had been handing out bottles of water to protesters when a grenade landed near her forearm. Suddenly, it detonated, according to witnesses.
"She was air lifted to County Medical Center in Minneapolis were she's currently undergoing extensive, hours-long surgery from injuries sustained from the blast," said a GoFundMe page raising money for her medical costs.
Initially, protesters feared the worst: Doctors would have to amputate her arm due to the explosion.
But Wayne Wilansky, Sophia's father, told CNN affiliate KFYR that amputation wouldn't be necessary even though the explosion "blew the bone out of her arm."
Wilansky noted his daughter, who might need as many as 20 surgeries to repair her forearm, still remained focused on the pipeline fight.
"Even though she's lying there with her arm pretty much blown off, she's focused on the fact that it's not about her, it's about what we're doing to our country, what we're doing to our native peoples, what we're doing to our environment," Wayne Wilansky said.
Police: We didn't fire grenades at protesters
On Tuesday, North Dakota State Patrol spokesman Lt. Tom Iverson told CNN affiliate KFYR that state troopers had not deployed a grenade or any other explosive against protesters on Sunday.
"There is no merit to that," Iverson said."But I assure the citizens of North Dakota ... that law enforcement is investigating this. All the facts will be out there."
The North Dakota Joint Information Center also released photos of improvised weapons that law enforcement said protesters used against them during the confrontation at Backwater Bridge.
Authorities said they recovered a punctured propane cylinder, rocks and glass jars, which they said are commonly used to make Molotov cocktails.
According to KFYR, police say protesters were seen running to the area where the explosion had happened. The group pulled a female from under a burned vehicle on the bridge, then fled, authorities said.
'There are many witnesses'
However, Wayne Wilansky questioned Iverson's contention that police refrained from using grenades.
"There are many witnesses," Wilansky said. "They have scrap metal, and the sheriff's office says they did it to themselves -- that they blew up their own bombs or something. That's ridiculous."
Despite the gruesome injury to Sophia Wilansky, protesters vowed to move ahead with further protests.
As for the pipeline, construction has stalled as the Corps of Engineers engages in talks with Native American leaders.