Officers searching a property in the south of the county have recovered a number of large Koi carp and goldfish which they believe may have been stolen.
A man was arrested following the search.
A spokesman for Lincolnshire Police said: “We have not had any reports of thefts from aquatic centres so the fish may be from someone’s private pond.
“We are asking pond-keepers to check their ponds and contact us if they believe they may have been the victim of theft.”
To report a theft, please call Lincolnshire Police on 101. If you believe the recovered fish may be yours and you would like further information, please email firstname.lastname@example.org.