Sea

The Eighth Doctor rows out to a sea. (PROSE: Dr. Eighth)

A sea was a large body of liquid.

Seas on Earth

According to Greek mythology, Poseidon was the god of the sea and earthquakes. (TV: Planet of Fire)

In 2006, the Slitheen family hid their spaceship in the North Sea and sent it to London as part of their plan to destroy Earth. (TV: Aliens of London / World War Three)

When the Second Doctor landed the TARDIS at Cape Arid, Australia in 2018, he immediately took off his coat and trousers and went for a swim; to the utter amazement of Jamie and Victoria. (TV: The Enemy of the World)

The TARDIS materialised on a schooner in the Caribbean Sea in 1800. When the Tenth Doctor and Martha Jones went out to explore, they were apprehended by the crew and nearly thrown overboard. (COMIC: Second Wave)

In 39 BC, the Eleventh Doctor, Amy Pond and Rory Williams arrived on a Roman ship in the Mediterranean Sea. The crew were unknowingly transporting a Gold Assassin to Cleopatra. (COMIC: Golden Slumbers)

Seas on other planets

Kandalinga was a world completely covered in sea. (PROSE: The Fishmen of Kandalinga)

A gang of pirates made their lair under the sea of an Earth-like planet. (PROSE: Ten Fathom Pirates)

Quinnis had a purple sea. (COMIC: A Religious Experience)

Thoros-Beta had a number of seas, including the Sea of Despair and Longing, the Sea of Sorrows and the Sea of Turmoil. (TV: Mindwarp)

Sskendass-giis was a dried up sea bed on the planet Mars, known in English as the Dead Ocean of the Forsaken. (PROSE: GodEngine) In the 22nd century, Mars had an artificial red sea. The sea on Mars, or more specifically, a life form that lived in the reflections of the sea, attacked a cruise ship to take over the bodies of the people on board for an hour. (COMIC: The Cruel Sea)

Sam Jones felt "the first twinges" of agoraphobia when she was on Hyspero, a planet with deserts and seas that seemed to go on forever. (PROSE: The Scarlet Empress)

The Barian Sea on Moldox had golden water, and the beaches formed from grains of ice. (PROSE: Engines of War)

There were several areas on the Moon called seas, including the Sea of Crises, the Sea of Ingenuity, the Sea of Nectar, and the Sea of Tranquility. (TV: Kill the Moon)

The seas of Marinus (TV: "The Sea of Death"), 16 Alpha Leonis One (PROSE: Eternity Weeps) and Endpoint were all composed of acid. (PROSE: Hope) Albraxiz had seas of hydrochloric acid. (PROSE: Grimm Reality)

The Silvasic Sea was the largest body of water on Dellah. (PROSE: Dry Pilgrimage)

The sea of an unnamed planet was home to a Klepton city. (COMIC: The Klepton Parasites)

Alternate timeline

In an alternate timeline during the Year That Never Was, the Saxon Master poisoned the Caspian Sea. (TV: Last of the Time Lords) Martha Jones visited it during her travels around the globe. (PROSE: The Story of Martha)