"The lake" was somewhere that Marty McFly and Jennifer Parker were planning to camp out at before their adventures with Dr. Emmett Brown, had only Marty possessed a vehicle like the Toyota Hilux 4X4 he saw at Statler Toyota downtown.
When Marty changed the past in 1955, it affected the future and the Hilux 4X4 was his. When Marty and Jennifer left for 2015, his family assumed that they had departed for the lake. When Marty returned home after 1885, they thought he picked up his Western wear at the lake. Whether Marty and Jennifer did eventually make it to the lake remains unrecorded.
While in 1885, Doc Brown may have been referring to the same lake to wait for it to freeze over in winter. Furthermore, Buford Tannen and his gang were camping next to a lake that could have been the same.
In 1986B, the lake was the location of a Math and Magic Competition that the Marty of that timeline attended.
Behind the scenes
- Considering how Marty says "up to the lake", it is likely located in the Sierra Nevadas, or even north of Hill Valley.
- Back to the Future (First mentioned)
- Back to the Future Part II (Mentioned only)
- Back to the Future Part III (Mentioned only)
- Back to the Future: The Game
- Back to the Future: The Game - Episode 3: Citizen Brown (Mentioned only)