WASHINGTON — Authorities smell something fishy on Long Island — and are deploying undercover agents to go after commercial fishermen who lie about how much fish they’re catching.

Last week, law enforcement officials charged a father and son in Southampton after they reported landing 210 pounds of fluke and inspectors found another 400 pounds in the hold and below deck.

“They just jumped on us. They come down pretty rough,” said John Berglin, the father who got busted.

The arrest was no fluke.

Jim Gilmore, director of the Marine Bureau of the state Department of Environmental Conservation, said officials scour reports that fishermen file with the feds.

“Suddenly, the numbers weren’t adding up,” he told The Post.