A woman accused of killing her fiancé by tampering with his kayak and then leaving him to drown in the cold and choppy waters of the Hudson River pleaded guilty on Monday to a reduced charge of criminally negligent homicide.

The case drew attention far beyond the area just north of New York City where the death occurred, as prosecutors described how a seemingly doting partner desperately called 911 for help after her fiancé disappeared only to tell investigators later that it “felt good knowing he was going to die.”

The woman, Angelika Graswald, 37, was awaiting trial for second-degree murder and faced a maximum sentence of life in prison. She was charged in April 2015, after her fiancé, Vincent Viafore, 46, vanished after his kayak capsized during a trip on the Hudson River. The authorities said that Ms. Graswald had removed a plug from the boat and knew that a locking clip that kept the paddle in place was missing.

The couple was returning on the evening of April 19 to the western shore of the Hudson from Bannerman Island, several miles north of West Point. The wind picked up, and Mr. Viafore, who was not wearing a life jacket or a wet suit, fell into the water. (His body was recovered in May.)