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.
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