[konming]

Here are all the sites underwater:

Diamond Corals 0 0 Air
Imprisoned Zephyr 2 1 Air
Pocket of Air 2 2 Air
Underwater Cave 2 3 Air
The Water Solstice 0 1 Astral
Seventh House on the Left 0 1 Astral
Arcane Gateway 2 2 Astral
The Iron Caverns 1 2 Astral
Basalt Pillars 2 2 Astral
Labyrinth of the Deeps 2 2 Astral
Pearl Stairway 2 3 Astral
The Crater 2 3 Astral
Gorge of Mystery 1 3 Astral
Ghoul Fish Cave 1 0 Death
The Wasted Sea 1 1 Death
Isle of Death 2 1 Death
Sunken Galley 1 1 Death
Dying Ground of the Whales 1 1 Death
The Sea of Dead Memories 1 1 Death
Reef of Sunken Ships 1 2 Death
Iron Cliff 1 0 Earth
Caves in the Deep 0 0 Earth
Isle of the Sea Fathers 0 0 Earth
Plateau of Shards 1 1 Earth
City of Stones 1 1 Earth
Mineral Fingers 1 1 Earth
Underwater Cliff 0 1 Earth
Basalt Halls 1 2 Earth
Basalt Statue 1 2 Earth
Long Lost Circle 2 2 Earth
Moving Sandbanks 1 2 Earth
The Basalt Forge 2 2 Earth
Firbolg Fortress 0 3 Earth
Gorge of Glowing Fish 1 1 Fire
Thermal Vent 0 1 Fire
Copper Cliff 1 1 Fire
Fire Rift 2 1 Fire
Magma River 2 2 Fire
Ancient Temple of the Deeps 1 1 Holy
Kelp Sea 2 0 Nature
Kelp Forest 0 1 Nature
Amber Beach Island 2 1 Nature
Sea Oak 0 1 Nature
Kelp Grove 1 1 Nature
Kelp Fortress 2 1 Nature
The Forest beneath the Waves 2 2 Nature
The Amber Halls 2 2 Nature
Forest of Amber Kelp 2 2 Nature
Coral Garden 1 2 Nature
Floating Forest 0 2 Nature
Cold Currents 0 0 Water
Troll Pit 2 0 Water
Clam Field 1 1 Water
Whispering Waters 1 1 Water
Depths Unnamed 0 1 Water
Glowing Depths 1 1 Water
Coral Reef 0 1 Water
Isle of Ice 1 1 Water
Dark Waters 1 1 Water
Falling Depths 1 1 Water
Academy Underneath 0 1 Water
Tower of Pearls 1 1 Water
Kraken Pit 2 2 Water
The Darkness 2 2 Water
Sentinent Current 2 2 Water
The Gate in the Deep 2 2 Water
The Hippocampoi Fields 2 2 Water
Coral Statue 2 2 Water
Man'o'War Breeding Ground 1 2 Water
Sunken Island 2 2 Water
Sunken Tower 2 2 Water
Shrine of the Shark Lords 2 3 Water
(thanks to domdb)

So you can see there are a 5 fire sites out of 73 total possible sites.