The Black Lake

• Type: Lake
• Location: On the grounds of Hogwarts School of Witchcraft and Wizardry, Scotland
• Owner/Residents: Giant Squid, Merpeople, Grindylows
• Key Features: Very deep and cold freshwater, inhabited by magical creatures, connected to Hogwarts plumbing, site of the Second Task of the Triwizard Tournament

The Black Lake, also known as the Great Lake, is a large, deep body of freshwater located to the south of the Hogwarts Castle. Its surface is often described as smooth and glass-like on calm days, but its waters are perpetually murky and cold, making unaided underwater exploration extremely difficult. The grounds surrounding the lake consist of sloping lawns that lead down to its shores. The path from Hagrid's hut runs along its edge, and on the opposite side, it is bordered by trees. The lake is an ancient and integral feature of the Hogwarts grounds, presumably existing since the school's founding. It is home to a variety of magical creatures, most notably a large colony of Merpeople who have a village in its depths and a resident Giant Squid, which is generally peaceful and has occasionally interacted with students. The lake is magically connected to the castle's plumbing system; Ginny Weasley revealed that she had flushed Tom Riddle's Diary down a toilet in Moaning Myrtle's bathroom, and it eventually found its way into the lake. Furthermore, the windows of the Slytherin Common Room look out into its green, eerie depths. Historically, the lake's most significant event in the modern era was serving as the venue for the Second Task of the revived Triwizard Tournament in 1995.

The Black Lake serves as a significant backdrop and event location throughout the series.

• First Arrival: First-year students traditionally cross the lake in a fleet of small boats, guided by Rubeus Hagrid, to get their first view of Hogwarts Castle.
• Prisoner of Azkaban: The lake's shore is the site of two pivotal moments. First, Harry Potter, Ron Weasley, and Hermione Granger wait there during the apparent execution of Buckbeak. Later, Harry casts a corporeal Patronus in the form of a stag across the lake to save his past self, Hermione, and Sirius Black from a swarm of Dementors.
• Goblet of Fire: The lake is central to the plot as the location for the Second Task of the Triwizard Tournament. The champions were required to dive to the bottom to rescue a “hostage” from the merpeople's village. During this event, Harry uses Gillyweed to breathe underwater, allowing readers a detailed view of the lake's environment and inhabitants, including Grindylows and the Merpeople.
• Order of the Phoenix: Harry Potter and his friends often study by the lake. It is here, while taking his O.W.L.s, that Harry has a vision of Voldemort torturing Sirius Black in the Department of Mysteries.
• Half-Blood Prince: The funeral of Albus Dumbledore is held on the shore of the Black Lake. He is laid to rest in a magnificent white tomb by the water's edge, a location of great solemnity and importance.
• Deathly Hallows: During the Battle of Hogwarts, Voldemort's disembodied voice booms across the lake to the castle's defenders. After the battle, the white tomb is broken into by Voldemort to steal the Elder Wand. Following the final victory, Harry, Ron, and Hermione sit by the lake, quietly contemplating their future.

• Merpeople Village: A settlement located on the lakebed in the centre of the lake. It consists of crude stone dwellings, some with gardens of aquatic plants, and is presided over by a large statue of a Merperson carved from a boulder. This was the location of the hostages during the Second Task.
• Kelp Forests: The lake contains dense patches of seaweed and kelp, which serve as hiding places for creatures such as the aggressive Grindylows.
• Albus Dumbledore's Tomb: While technically on the shore, the white tomb is the lake's most prominent man-made feature. It served as the final resting place of Albus Dumbledore and, briefly, the Elder Wand.

• In the film adaptations, the Black Lake is depicted as being surrounded by much more dramatic and mountainous terrain than described in the books (film).
• Several real-life Scottish lochs were used for filming scenes involving the Black Lake, including Loch Shiel, Loch Eilt, and Loch Morar (film).
• J.K. Rowling has confirmed that the Giant Squid is a genuine, non-magical creature (in the sense that it is not an apparition or magical construct), though its size and longevity are exceptional (J.K. Rowling interview).
• The video game version of Harry Potter and the Goblet of Fire features a Second Task level that expands the lake's environment with various puzzles and hostile creatures not mentioned in the book (video game).