The Great Lake (alternatively known as the Black Lake) is a large body of water located to the south of Hogwarts Castle. It is about half a mile in diameter and the castle's plumbing network drains into it.
Every school year at Hogwarts, after the Hogwarts Express arrives at Hogsmeade Station, Rubeus Hagrid (or a substitute) calls the first years to follow him to the lake shore and the magic boats. Whereupon Hagrid occupies one boat and each other boat carries up to four students. The boats then self-propels across the lake to a dock under Hogwarts Castle as per tradition. (at the start of the 1994–1995 school year, first year Dennis Creevey said he fell into the lake and the Giant Squid pushed him back into a boat). Upon reaching the castle, Hagrid and the first years disembark and climb the stairs to the lawn, entering the castle through the front doors. First years then waited until summoned into the Great Hall to get Sorted into their houses. At the end of their first year, students take the boats back to Hogsmeade Station, while most older students ride down the lane in carriages.
Students from Durmstrang Institute arrived at Hogwarts on their enchanted boat via the Great Lake. As part of the Second Task of the Triwizard Tournament, the four champions Harry Potter, Fleur Delacour, and Cedric Diggory, and Viktor Krum had to swim in the lake for one hour to rescue something that was taken from them. Harry used Gillyweed to be able to breath underwater, while Cedric and Fleur used the Bubble-Head Charm, and Krum partially Transfigured himself into a Shark.
It is home to a Giant Squid, Grindylows, and a colony of Merpeople. The lake was also used as the site of the Second Task of the Triwizard Tournament. The Slytherin common room is beneath the lake, accessed through an entrance in the school dungeons. The Chamber of Secrets is also thought to be beneath the lake. At some point, Neville Longbottom's pet toad, Trevor, escaped into the lake, joining other toads that lived there.
The lake is often said to be very cold, but Viktor Krum was known to have swam in it, wearing nothing but swimming trunks, apparently not affected by the low temperature (although this was probably due to the fact that his school, Durmstrang, is located in a place that is even colder).
Lily Evans and her friends were also said to dangle their legs over the water, which could mean that there were no rules whilst they were in school against swimming in the lake.
Behind the scenes
- In the Harry Potter films, the Great Lake is portrayed by Loch Shiel.
- In the films, the lake is known as "The Black Lake."
- In LEGO Harry Potter: Years 1-4, the lake has quays.
- In the films, Dumbledore's body is placed on a small island in the middle of the Great Lake. After this, in 1998, Voldemort accesses Dumbledore's grave and takes the Elder Wand from it. It is possible that the island was first seen in in the film adaptation of Harry Potter and the Prisoner of Azkaban.
- In an early draft of Harry Potter and the Chamber of Secrets, J.K.Rowling planned to have Harry and Ron crash the car into the lake and be introduced to the merpeople at that point. 
- Harry Potter and the Philosopher's Stone (First appearance)
- Harry Potter and the Philosopher's Stone (film)
- Harry Potter and the Philosopher's Stone (video game)
- Harry Potter and the Chamber of Secrets
- Harry Potter and the Chamber of Secrets (film)
- Harry Potter and the Chamber of Secrets (video game)
- Harry Potter and the Prisoner of Azkaban
- Harry Potter and the Prisoner of Azkaban (film)
- Harry Potter and the Prisoner of Azkaban (video game)
- Harry Potter and the Goblet of Fire
- Harry Potter and the Goblet of Fire (film) (First identified as Great Lake)
- Harry Potter and the Goblet of Fire (video game)
- Harry Potter and the Order of the Phoenix
- Harry Potter and the Order of the Phoenix (film)
- Harry Potter and the Order of the Phoenix (video game)
- Harry Potter and the Half-Blood Prince
- Harry Potter and the Half-Blood Prince (film)
- Harry Potter and the Half-Blood Prince (video game)
- Harry Potter and the Deathly Hallows
- Harry Potter and the Deathly Hallows: Part 1 (Appears in vision(s))
- Harry Potter and the Deathly Hallows: Part 2
- Harry Potter and the Deathly Hallows: Part 2 (video game)
- Harry Potter: A Pop-Up Book
- LEGO Harry Potter: Building the Magical World (Mentioned only)
- LEGO Harry Potter: Characters of the Magical World (Merpeoples' grotto and various mentions)
- Harry Potter: Quidditch World Cup
- LEGO Harry Potter: Years 1-4
- LEGO Harry Potter: Years 5-7
- Harry Potter for Kinect
- Pottermore (Mentioned only)
- Harry Potter LEGO Sets (Merpeoples' grotto)
- Harry Potter: The Character Vault
- Harry Potter: The Creature Vault
Notes and references
- ↑ Pottermore Insider - "It's time to pass the magic on with the new Bloomsbury Harry Potter books"
- ↑ Harry Potter and the Prisoner of Azkaban (video game) - see this image
- ↑ Harry Potter and the Goblet of Fire (film)
- ↑ 2007 PotterCast Interview
- ↑ Pottermore information on toads (transcript available here)
- ↑ Black Lake in Wikipedia
- ↑ Pottermore