This is the heroic moment a policeman waded through filthy water to rescue a dog trapped in a canal.

A passerby heard the canine's desperate barks coming from the channel in Valencia, Spain, on June 16.

Upon checking, the animal was seen struggling against the current in a 45-metre underground section, crying out for help.

Concerned neighbours contacted emergency responders from the Guardia Civil to assist in the rescue.

Dramatic footage shows a kindhearted sergeant emerging from the canal, still in uniform, carrying the distressed dog.

Following the rescue, the four-legged pet was taken to a nearby veterinarian. Its microchip was scanned, identifying its owner, a resident of Alzira.

The pooch was joyfully reunited with its family.