In 2016, protests against the Dakota Access Pipeline in North Dakota — led by the Standing Rock Sioux tribe — drew attention to the impact of the oil and natural gas industries on the environment. The battle is ongoing, despite an executive order signed by President Donald Trump to allow the pipeline’s construction.

The heightened awareness of the Dakota Access Pipeline draws attention to other pipeline projects throughout the United States. Across the country right now, over 20 proposed pipelines would run through indigenous land and endanger water sources, including wetlands and aquifers. Then, when spills happen, energy companies responsible for the pipelines may not take full responsibility for cause or cleanup.

Here are six controversial pipeline projects to keep an eye on.

Line 3 in Minnesota

One of the largest inland oil spills in U.S. history happened along the Line 3 oil pipeline when it spilled 1.7 million gallons of crude oil near Grand Rapids, Minnesota, in 1991. Built between 1962 and 1967, this corroded pipeline is over five decades old and pumps 390,000 barrels of oil per day.

Now, Canadian company Enbridge Energy plans to build a new pipeline to replace its old Line 3 oil pipeline, which would transport oil across northern Minnesota to Superior, Wisconsin, including through Ojibwe treaty territory. However, activists are organizing to persuade Minnesota officials to deny the permit for the pipeline and stop the project.

The White Earth Nation, Red Lake Nation, Leech Lake Band, and Fond du Lac Ojibwe Band have been joined by activist groups to participate in public meetings about the pipeline. The company decided to reroute the pipeline around a wild rice lake used by tribes after the White Earth Nation voiced their concerns, but activists still say the pipeline poses a high risk for water pollution, as does the company's plan to leave the old, deteriorating pipeline in place even after the new one is constructed.

More public hearings in front of an administrative law judge will take place in the fall, and the Minnesota Public Utilities Commission will make a final decision next April. If approved, the pipeline could operate by the end of 2019 and could carry up to 760,000 barrels of oil a day.

Keystone XL in Nebraska, South Dakota, and Montana

This project was previously blocked in 2015 by the Obama administration, but the Trump administration gave the green light to the Keystone XL by signing an executive order for its construction in January. Keystone XL still has a major obstacle though: Nebraska.

The Keystone Pipeline runs from Canada to Texas, but Nebraska has yet to approve the proposed extension route of the Keystone XL, which would go through Montana, South Dakota, and Nebraska. Native American tribes — including the Ponca Tribe and Sioux Tribe of Nebraska — worry that a leak would contaminate sources of water such the Ogallala aquifer beneath the Great Plains, which is one of the world’s largest sources of groundwater. Protests, including a campaign to build solar panels in the pipeline's path, called Solar XL, have already emerged.

In addition, on July 7, Keystone XL opponents also said that they may appeal a South Dakota judge’s decision to uphold state regulators’ approval for the pipeline in their state.

This pipeline route would carry 830,000 barrels of oil a day. The State Department estimated that the project will lead to tens of thousands of temporary positions, but just 50 permanent jobs.