Generally, lightning can travel for 20 feet through water before dissipating. How far the charge travels depends on the intensity of the lightning, topography of the water, salinity and temperature. Lightning does not penetrate deep into water, but the charge disperses in all directions, favoring the surface.
Despite water being a good electrical conductor, lightning doesn’t travel further in water than over land. On the ground, electrical current spreads out in streams, and this allows it to go farther than if it dissipated uniformly through the water. The uniform dissipation of the electrical charge means that the total affected area is larger than on land, but the distance at which the charge remains dangerous is significantly smaller.
Electrical currents take the path of least resistance, which means that it travels through saline water rather through the body of any marine animals, swimmers or scuba divers. However, lightning also seeks the shortest path to the ground and will strike any objects sticking out over the water surface.
According to Science blogs, lightning can generate up to 300 million volts and 10, 000 to 20, 000 amps. A lightning strike at the surface can produce powerful sound waves up to 260 decibels and cause some local warming of water.