A Nensi phenomenon is one that occurred on the USS Stargazer under the command of Captain Jean-Luc Picard in 2354.

The phenomenon caused the warp nacelle's pressure to build until a point of explosion, threatening the starship. The ship was saved by Jack Crusher and Peter Joseph by severing the nacelle of the ship. While attempting to sever the nacelle with hand phasers, Crusher was killed in an explosion that occurred after the nacelle was disconnected from the ship. (TNG novel: Reunion)