If you're thinking of the Tunguska event in Siberia...
it happened in 1908 and exploded with a force estimated at 8-10 megatons, almost a thousand times the force of the Hiroshima bomb. That's the last big one that I know about. No doubt there have been water impacts, probably smaller than Tunguska, since then. I remember seeing news reports about a rogue wave that washed ashore in Florida several years ago. If I remember correctly, one woman died in that event. I read later that one researcher believes the wave was caused by a water impactor.