As Europe's energy costs skyrocket, Russia is burning off large amounts of natural gas, according to analysis shared with BBC News.
They say the plant, near the border with Finland, is burning an estimated $10m (£8.4m) worth of gas every day.
Experts say the gas would previously have been exported to Germany.
Germany's ambassador to the UK told BBC News that Russia was burning the gas because "they couldn't sell it elsewhere".
Scientists are concerned about the large volumes of carbon dioxide and soot it is creating, which could exacerbate the melting of Arctic ice.
The analysis by Rystad Energy indicates that around 4.34 million cubic metres of gas are being burned by the flare every day.
It is coming from a new liquefied natural gas (LNG) plant at Portovaya, north-west of St Petersburg.
The first signs that something was awry came from Finnish citizens over the nearby border who spotted a large flame on the horizon earlier this summer.
Portovaya is located close to a compressor station at the start of the Nord Stream 1 pipeline which carries gas under the sea to Germany.
Supplies through the pipeline have been curtailed since mid-July, with the Russians blaming technical issues for the restriction. Germany says it was purely a political move following Russia's invasion of Ukraine.
But since June, researchers have noted a significant increase in heat emanating from the facility - thought to be from gas flaring, the burning of natural gas.
While burning off gas is common at processing plants - normally done for technical or safety reasons - the scale of this burn has confounded experts.
"I've never seen an LNG plant flare so much," said Dr Jessica McCarty, an expert on satellite data from Miami University in Ohio.
"Starting around June, we saw this huge peak, and it just didn't go away. It's stayed very anomalously high."
Miguel Berger, the German ambassador to the UK, told BBC News that European efforts to reduce reliance on Russian gas were "having a strong effect on the Russian economy".
"They don't have other places where they can sell their gas, so they have to burn it," he suggested.
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