Fisher CZ6, sound fading ?

[Forager]

Hi all.
I was out on the beach yesterday with my trusty old CZ6 . On emersing the coil in to the sea I later noticed the sound fading on any target. Do you think water has somrhow got in or just pure coincidence? . I put new batteries in so don't think its a power problem. I switched the machine off and rr tried 10 minutes later .. same. Checking the coil and no obvious cracks. Hoping someone on here can help !