Ability Score Increase

Your Strength score increases by 1, and you Constitution score increases by 3.

Age

Dragons are practically immortal, making it hard to find a deficit end to their life. The oldest ever recorded was 13,000 years old, though it seems to be nearing it's death.

Alignment

Any

Size

As a water dragon your size is small(for a dragon). 

Draconic Ancestry

You have a dragon breath weapon and resistance. Choose one type of dragon from the Draconic Ancestry table. Your breath weapon and damage resistance are determined by the dragon type, as shown in the table.

Draconic Ancestry

Breath Weapon

You can use your action to exhale destructive energy. Your draconic ancestry as a water dragon determines the size, shape, and damage type of the exhalation. When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry. The DC for this saving throw equals 8 + your Constitution modifier. A creature takes 6d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 9d6 at 6th level, 12d6 at 11th level, and 15d6 at 16th level. After you use your breath weapon, you can’t use it again until you complete a short or long rest.

Dragon Hide

You have resistance to the damage type associated with heat and fire but you are weaker to electrical based attacks and earth elements.

Languages

You can speak, read, and write and Draconic and Merfolk.

Darkvision

You have darkvision to 60 feet. 

Bite

You are proficient with your bite. It is a natural melee weapon that deals 1d10 plus strength modifier piercing damage.

Shapechange

You begin to master your innate magical abilities as you age. (start out as a "dragon born" and slowly be able to turn into your true dragon form as you lv up.)