A ban on bottled water in 23 national parks prevented up to 2m plastic bottles from being used and discarded every year, a US national park service study found. That is equivalent to up to 326 barrels of oil worth of emissions, 419 cubic yards of landfill space and 111,743lb of plastic, according to the May study.

Despite that, the Trump administration reversed the bottled water ban just three months later, a decision that horrified conservationists and pleased the bottled water industry.

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“The bottled water industry has led a years-long campaign against this commonsense policy, all to protect its bottom line,” said Lauren DeRusha Florez, an associate campaign director at Corporate Accountability International.

“The fact that Trump administration officials knew the benefits of this policy back in May but still decided to rescind it last month sure looks to me like the bottled water industry’s lobbying dollars at work,” she said.

The plan to curb pollution in America’s most famous wilderness areas was spurred when arguably its most famous park, the Grand Canyon, banned the sale of plastic water bottles in its gift shops, according to the report. Approximately 331 million people visit US national parks each year.

The program was meant to support a “life cycle” approach to plastic, which activists say is the largest global threat to the environment behind climate change. One million plastic bottles are sold per minute, according to a Guardian analysis. The top six drink companies in the world use an average of just 6.6% recycled plastic.

At the same time, new research has shown that plastics which find their way into the sea have entered the food supply. Scientists have found plastic particles in sea salt, honey, fish, beer and tap water.

The National Park Service released the report in response to a Freedom of Information Act request. In a cover sheet to the report, the agency said it was originally developed to help management make decisions, but that the agency has “lacked the data necessary to ensure the report’s findings”.

The agency started allowing parks to ban bottled water in 2011. Since then, the bottled water industry argued that the ban was unfair and eliminated a healthy beverage option, even though hydration stations with free water were installed in parks.

When the National Park Service ended the ban in August, it echoed an industry argument: “It should be up to our visitors to decide how best to keep themselves and their families hydrated during a visit to a national park, particularly during hot summer visitation periods,” said the acting service director, Michael Reynolds.