Lincolnshire Police are investigating the deaths of 26 sheep in a field next to the A46 near Market Rasen.
The sheep were led from a field in between Starks Lane and Osgodby Top to a water filled dyke on the evening of January 5.
Police do not know how all the sheep were herded into the water.
PCSO Neal Evans said: “Did you see any suspicious vehicles or any stray dogs in the area or have your dogs been missing and returned in a dirty state?”
A spokesperson for Lincolnshire Police added: “There isn’t any evidence that this has been caused by dogs or that it is a criminal act, according to the reporting officer. It seems the sheep have ended up in a water filled ditch and have drowned or suffocated.”
Anyone with information should get in touch with the force on 101, quoting incident 168 of January 6.