Typical sea serpents are 60 feet in length and weigh 4,500 pounds, but their upward size limit is unknown. Certainly, the sea is a vast and mysterious place more than capable of supporting whales and other such leviathans, and tales of sea serpents that exceed lengths of 300 feet or more are not unheard of. You can generate statistics for a sea serpent of such tremendous size by applying the advanced simple template or the giant simple template to the statistics presented here. Alternatively, you can advance this sea serpent to Colossal size, increasing its Hit Dice to 25 and its CR to 18.