Something fishy is going on at an ultra-liberal Upper West Side synagogue.

Congregation B’Nai Jeshurun on West 88th Street canceled lox — and then reeled in its decree after it realized it was swimming against the tide of public opinion.

Rabbi Shuli Passow, the synagogue’s director of community engagement, told congregants in a Sept. 8 post that the fish would be yanked from its catering options so “we can do our part to reduce the environmental impact of pollution and overfishing.”

One online kibitzer dubbed the move a “loxdown” and another mused “What will they ban next, gefilte fish?”

“It’s a little meshugga, a little meshugga,” said Gary Greengrass, third generation owner of famed smoked-fish emporium Barney Greengrass on the Upper West Side. “There’s other things to be focused on.”

Emily Caslow, a member of the fourth-generation ownership of Brooklyn-based Acme Smoked Fish — the city’s largest purveyor — and an Upper West Sider, quickly stepped forward to school the synagogue about the origins of the salmon.

“I reached out to let them know that the information shared about lox was inaccurate,” Caslow said.

On Monday, the synagogue issued a “correction,” claiming it didn’t realize most lox was made from farmed Atlantic salmon.

“We thank those who brought this error to our attention, giving us the opportunity to correct our mistake,” the synagogue wrote in a post to its website.

“Second, some felt that we implied that eating lox is immoral or that BJ is boycotting lox or lox providers. This could not be farther from the truth,” the statement said.

Lox can now be served if congregants shell out for the kiddush, a light meal after Sabbath services during which bagels and various toppings are traditionally served. 

But there was a catch.

The synagogue said it would refrain from offering the salty specialty when it pays for the kiddush, now citing increasing costs and “our desire to include more plant-based offerings at community meals.”