The Department of Defense said the S-shape, which the weather bureau's radar detected off the coast of West Australia Wednesday, was caused by a training exercise involving ships and aircraft preparing a Navy warship for operational deployment, the Australian Broadcasting Corp. reported Thursday.
"The environmental conditions over the West Australian coast at the time of the activity provided a unique opportunity for this routine activity to be visible on the weather radar display," a department spokesman said. "This exercise is ongoing."
The West Australia Weather Group earlier took to Twitter and dubbed the shape the "RottNess Monster."
"Nice that our pet #RottNessMonster has avoided the shark baits. Her name is Susan & she likes to eat plankton," the tweet read.