Thank you all for your input and comments.
Cable is from a dish on the house. Water is from a well on the premises, haven't checked the ground current on that possibility. This home is quite a distance from other structures, the closest house is 1/4 mile away and on its own xfmr. A local ground would have to be bare wire into the lake as the shoreline is at best a few feet of gravel over bedrock. The dock is moored to an almost vertical cliff face. I have current flow through the steel cables extending down to the downriggers that space the dock from the shore.
