Here is a sample I brewed up.
Large Dragon (Water)
Hit Dice: 16d12 + 64 (168 hp)
Speed: 60 ft., fly 200 ft. (poor), Swim 90 ft.
Armor Class: 26 (-1 size, +16 Natural, +1 Dodge), touch 10, flat-footed 26
Attack: Bite +21 melee (2d6+6)
Full Attack: Bite +21 melee (2d6+6) and 2 claws +21 melee (1d8+3) and 2 wing buffets +21 melee (1d6 +3)
Space/Reach: 10 ft./5 ft. (10 ft. with bite)
Special Attacks: Breath weapon, frightful presence, spell-like abilities, spells
Special Qualities: Blindsense, charm avian, damage reduction 5/magic, darkvision 120 ft., immunity to cold, immunities paralysis, sleep, keen senses, mistsight, purify water, Resistance 10/acid, SR 16 waterbreathing
Saves: Fort +14, Ref +10, Will +12
Abilities: Str 23, Dex 10, Con 19, Int 13, Wis 15, Cha 14
Skills: Appraise +20, Diplomacy +4, Knowledge (nature) +11, Listen +21, Search +20, Sense Motive +19, Spot +21, Survival +4 made in aboveground natural environments (aquatic, desert, forest, hill, marsh, mountains, or plains) and to follow tracks. Use Magic Device +12
Feats: Cleave, Dodge, Flyby Attack, Multiattack, Improved Multiattack, Power Attack
Environment: Rivers and lakes
Challenge Rating: 10
Treasure: Double Standard
Alignment: Neutral Good
Advancement: 17-20 HD (Large) 21-32 HD (Huge)
Level Adjustment: —
Autumnal Dragons have pale gold bodies tinged with reddish brown leaf-like scales along their backs. A prodigious set of elk-like antlers protrude from their heads. They possess serpentine bodies and long thin wings. Despite their frail appearance, autumnal dragons are fierce fighters.
They rarely come into contact with Humanoids, preferring the solitude of rivers that flow through ancient secluded forests.
A typical autumnal dragon is 16 feet long and weighs 1,200 pounds.
Autumnal dragons speak Common, Dragon and Sylvan.
Breath Weapon (Su): An autumnal dragon can breathe a cone of freezing mist that does 9d8 points of cold damage unless a successful Fortitude save (DC 24) is made for half damage. In addition, the mist obscures all sight, including darkvision, beyond 5 feet. Creatures 5 feet away have concealment (attacks by or against them have a 20% miss chance). Autumnal dragons are immune to the mist and can see normally through it. The magical mist lingers for 1d4+1 rounds regardless of wind conditions, even magically induced conditions. Underwater, the mist appears as obscuring bubbles. The save DC is Constitution-based.
Blindsense (Ex): Dragons can pinpoint creatures within a distance of 60 feet. Opponents the dragon can’t actually see still have total concealment against the dragon.
Charm Avians (Sp): An autumnal dragon can use this ability three times per day. It works as a mass charm spell that affects only avian animals. The dragon can communicate with any charmed avian as though casting a speak with animals spell. This ability is the equivalent of a 1st-level spell.
Frightful Presence (Ex): An autumnal dragon can unsettle foes with its mere presence. The ability takes effect automatically whenever the dragon attacks, charges, or flies overhead. Creatures within a radius of 90 feet are subject to the effect if they have fewer HD than the dragon. A potentially affected creature that succeeds on a Will save (DC 20) remains immune to that dragon’s frightful presence for 24 hours. On a failure, creatures with 4 or less HD become panicked for 4d6 rounds and those with 5 or more HD become shaken for 4d6 rounds. Dragons ignore the frightful presence of other dragons. The save DC is Charisma-based.
Keen Senses (Ex) An autumnal dragon sees four times as well as a human in shadowy illumination and twice as well in normal light. It also has darkvision out to 120 feet.
Mistsight (Ex): Autumnal dragons can see through fog, mist, and murky water as if they were perfectly clear, ignoring the miss chance for these obstructions, up to its normal range of vision. They can even see through magical mists and fogs.
Purify Water (Sp): Once per day an autumnal dragon can purify 10 cubic feet of water, making still water flow freely, clean, and able to support animal life. This ability makes liquids containing water potable. Magic items (such as unholy water) and items in a creature’s possession must succeed on a Will save (DC equal to that of the dragon’s frightful presence) or remain fouled. This ability is the equivalent of a 1st-level spell. Its range is equal to that of the dragon’s frightful presence (60 feet).
Spells: An autumnal dragon knows and casts arcane spells as a sorcerer of half its Hit Dice, gaining bonus spells for a high Charisma score. The sample autumnal dragon casts spells as an 8th level Sorcerer. Spells it can cast are 6/7/6/3/3. Typical spells it knows (8/5/3/2/1):
0—arcane mark, daze, detect poison, detect magic, flare, ghost sound, mending, ray of frost, read magic;
1st—alarm, shield, unseen servant, identify, true strike x3;
2nd—alter self x2, protection from arrow x2, resist energy x2;
3rd— dispel magic x3, explosive runes x3;
4th—remove curse x3.
Spell-Like Abilities (Sp): 3/day—expeditious retreat; 1/day—summon swarm (birds only).
Water Breathing (Ex): An autumnal dragon can breathe underwater indefinitely and can freely use its breath weapon, spells, and other abilities while submerged.
Skills: Appraise and Use Magic Device are class skills for autumnal dragons.