GFCI by itself is not enough. While GFCI protects a single outlet, it does not protect against other electrical sources such as boats, power providers, neighboring docks, or the very cable powering the GFCI outlet.

Electricity seeks the path of least resistance, and human and pet bodies conduct electricity with less resistance than fresh water. This is not usually the case in salt water.

Most electric shock drownings occur when low-level alternating current from boats, docks, or lights "escapes" into the water, shocking people in the water and paralyzing them so they can’t swim or help themselves.

The exact length that electricity can travel in water varies depending on the source, structures in the water, and water clarity and sediment levels. In some test conditions, electricity has reached dangerous levels at more than 300 yards from the source.

Animals are susceptible to ESD just like humans.

An inspection indicates your dock is up to code at that moment in time. Various things can cause wiring on your dock to wear out after the inspection, including wildlife, weather, dock motion, etc.