Islanders reported seeing the Coypu, which looks like a large rat, near Rozel earlier in the week.
The rodent is an invasive, non-native species.
It's not currently clear how the Coypu got into the island.
The animal was culled and eradicated in the UK in the 1980's because they were damaging flood defences and crops.
Jersey Government's Natural Environment team are urging islanders not to approach the rodent if they see it but to instead report it on 441674 or the duty officer on 441617 out of office hours.

Committee calls for Deputy Philip Ozouf's suspension
Baby sloth at Jersey Zoo orphaned as mother unexpectedly dies
DFDS contract reveals termination clause and performance penalties
French racing trimaran winched ashore off Guernsey
Ballet d’Jèrri returns to Opera House tonight
Jersey's new Bailiff sworn in
JT Group acquires Isle of Man's leading telecoms provider
Nude Dunes planning appeal dismissed