Fish Finders Gone Wacko

Just wondering if anyone else has run into this. South of Carmel Point at approx 36 32' 06" and 121 55' 58" both my and my partner's fish finder quit working. As soon as we paddled a little north they started working again. Anyone ever have that happen? I thought maybe it was becuase we were in the Carmel Canyon and were deeper than 600' which is the max on our fish finders but according to my GPS and my nautical chart we never got close enough to the area that is that deep......