The one that zipped over the US in 1972...
Would have hit the ground with the force of a Hiroshima atomic bomb if it
had not skipped out of Earth's atmosphere.
As another note, this obviously unannounced event was witnessed by a US
military satellite, thousands of people on the ground, photographed, and
even filmed, all in the age before cell phones and video cams.
So yes, the odds of a big space rock hitting water are higher than on
land, but it only takes one to hit a city to make a difference. Or even
if a Tunguska class event hit over a remote land region again, it might
still trigger a nuclear response.