Feds say ROBERT F. KENNEDY, JR. and his brother Max’s so-called good deed was a violation of strict federal law.

The Kennedy Bros. thought they were going to get some “good vibrations” by freeing an entangled 500 pound sea turtle but NOPE.

John Bullard of the National Oceanic and Atmospheric Administration Division of Fisheries  spoke to brothers Max and Robert F. Kennedy Jr. about their rescue of the gargantuan turtle in Nantucket Sound over the July Fourth weekend.

The trapped sea gargantuan, a leatherback turtle, became entangled with a buoy line wrapped around its head.

The eco-conscious Kennedys swam to the turtle’s rescue and freed it from a possible watery grave.

But NOAA’s Bullard told the Cape Cod Times the Kennedy rescue was a violation of the Endangered Species Act.

Bullard said only the Provincetown Center for Coastal Studies is certified to handle endangered sea turtles.

Robert Kennedy later said, posting on NOAA's website, that he now realizes what they did was "pretty risky."