"It's weird — she had never done this before — she ran into a pipe," Cindy McCain told The Arizona Republic. "You know, we have a series of ponds on our property ... and she ran into the pipe and she got stuck."
She added that Burma "drowned, and eventually, her body came out the other end of the pipe."
"It's devastating. She was John's dog, period, and so what makes me feel better is I know she's with him now," she said of Burma.
Meghan McCain, daughter of the 2008 GOP presidential nominee and current co-host of ABC's "The View," wrote on Instagram that the dog "was absolutely and truly devoted to him."
“She would never leave his side, followed him around every single step when he would walk around our ranch, slept by his side every night and we always said Chesapeake bay retrievers were the most affectionate breed of dogs,” she continued.
McCain spent the last year of his life with the beloved Chesapeake Bay retriever. He died in August after a battle with brain cancer.
Fox News' Kathleen Joyce and The Associated Press contributed to this report.