Two minor additions (how did I miss this thread first time round).

If sea-water is a good conductor, then I would have visualised it as a Faraday cage with rather thick walls. Certainly I would expect the charge to disperse radially in a hemisphere from the point of strike, with the current density dropping off in an inverse-squared way.

Talking to electrical transmission engineers (as I often have to), I hear there is a specific gait they adopt. Some medium voltage overhead cables are not fitted with open-circuit protection breakers, and dry ground is often not conductive enough to blow overcurrent protection either. If they have a broken live cable lying on the ground, they approach it (in rubber wellies) using shorter and shorter steps to limit the voltage gradient across the length of one stride. Also, it is often observed that cattle whose long axis is oriented in line with the cable end are much more likely to die than those standing sideways on at the same distance.