Hisgalus 8:10-11

And the malach hashlishi (third angel) sounded his shofar; and there fell out of Shomayim a kokhav gadol (great star) blazing as a torch and it fell on a third of the rivers and on the wells of mayim (water). And the name of the kokhav (star) is said to be “Wormwood,” and a third of the mayim became bitter wormwood, and many of the Bnei Adam died from the mayim because the mayim were made bitter.