Neither species in the movie can achieve anything remotely like the size depicted. Current evidence suggests that megalodons topped out at between forty-five and sixty feet. The largest crocodillian on record (Sarcosuchus imperator) has only been found to be in the vicinity of forty feet long.
The trick with the Turkey Point Nuclear Power Plant is impossible to have achieved, for two reasons. One, the energy sparking outwards had nothing to leap to, which would've prevented it from arcing like that in the first place. Second, most power lines are insulated to prevent such an overload from occurring in any event.