Oceanus Dragon

(From 3.5e Draconomicon: The Book of Dragons - 2003):

The Oceanus dragon protects travelers along the River Oceanus, which connects the Upper Planes in the same manner that the River Styx links the Lower Planes, while jealously guarding its domain against evil creatures of all kinds. 

Oceanus dragons appear much like great winged eels, with relatively short limbs ending in webbed fingers. Though capable of flight, most Oceanus dragons prefer life in the water to that in the air. 

The typical lair of an Oceanus dragon is a hidden cave, either along a riverbank or completely underwater. Most Oceanus dragons spend little time in their lairs, instead patrolling a stretch of river in search of good-aligned creatures in need of assistance or evil creatures in need of punishment. 

Oceanus dragons speak Celestial, Draconic, and Aquan. 

Combat: Oceanus dragons prefer to end fights quickly, using their tranquility breath weapon and spell-like abilities to neutralize foes. However, they aren’t afraid to go toe-to-toe with particularly resistant opponents, using their lightning breath weapon, smite evil ability, and prodigious melee attacks to make short work of their enemies. 

Young and older Oceanus dragons’ natural weapons are treated as magic weapons for the purpose of overcoming damage reduction. 

Breath Weapon (Su): An Oceanus dragon has two types of breath weapon, a line of lightning or a cone of tranquility gas. Creatures within the cone must succeed on a Will save or become dazed for 1d6 rounds plus 1 round per age category of the dragon. Both breath weapons function normally underwater. 

Smite Evil (Su): Once per day an Oceanus dragon can make a normal attack to deal extra damage equal to its HD total against an evil foe. 

Spell-Like Abilities: At will—detect evil; 3/day—control water, holy smite, water breathing; 1/day—control winds, dispel evil, holy word. Amphibious (Ex): Although Oceanus dragons are aquatic, they can survive indefinitely on land. Water Breathing (Ex): An Oceanus dragon can breathe underwater indefinitely and can freely use its breath weapon, spell-like abilities, and other abilities while submerged.