The offshore natural gas pipeline from Vyborg in Russia to Greifswald in Germany will double the amount of Russian gas arriving in Germany.
Russian energy giant Gazprom, which is behind the pipeline, already accounts for around one third of European gas supply.
The US President has previously expressed his disapproval, threatening to sanction European companies investing in the pipeline as early as October.
But responding to journalists’ questions ahead of a meeting with his Polish counterpart Andrzej Duda today, the US President issued his latest attack.
He stated: “Germany is paying Russia billions and billions of dollars, which, frankly speaking, we deem inappropriate.
“We never thought it was appropriate, and, certainly, this is very bad for the German people.”
Nord Stream 2 has also come under fierce criticism from some European nations including Ukraine, which stands to lose billions of dollars every year in transit fees.
Ukraine President Petro Poroshenko said the project is “political bribe money for loyalty to Russia”.
He told German business paper Handelsblat the pipeline holds “no economic justification” but German Chancellor Angela Merkel has defended the pipeline by saying it is a purely “economic project”.
Mr Poroshenko added Russia is an “extremely unreliable partner” in energy provision.
He also suggested modernising the gas transit through Ukraine instead of going along with the Nord Stream 2 pipeline.
Mr Poroshenko said: “There is a Ukrainian transit pipeline, which is much cheaper.
“It can be easily and profitably modernised. One can significantly modernise the transit line through Ukraine without huge investments.”
Mass opposition to the pipeline has also come from Angela Merkel’s own political party.
High-ranking German politicians from Mrs Merkel’s Christian Democratic Union (CDU) party, the environmentalist Greens and the pro-business Free Democratic Party all from Germany, warned in February against allowing the pipeline to go ahead.