The Third Trumpet is similar to the Second.

A great star falls to earth burning as a lamp
and it strikes the rivers.

A falling or fallen star, can literally be a falling
meteor or meteorite. The object is spoken of
as "it" meaning something impersonal. It
and its vapor puts something poisonous in
the waters killing those who drink it. This
one is called "Wormwood", named after a
bitter poisonous herb.