Members of the public have been asked to stay away from the scene of an incident at the River Bush in Bushmills.
It follows the recovery of what are believed to be items of stolen property.
The police operation, which began yesterday (Wednesday), is in the vicinity of the footbridge, which is closed as are parts of the river banks.
Police have recovered property suspected to have been stolen in a recent burglary and are conducting a search of the river to ensure everything has been found.
They are advising people, especially those intending to fish, to stay away from the scene until further notice.