Magab Lake was a lake on the planet Acamar III.
The Acamarian Wor Feighn accidentally drowned while swimming in this lake.
In 2366, this lake was mentioned in the death records archives, which were accessible to the crew of the USS Enterprise-D via the Acamarian planetary database.(TNG: "The Vengeance Factor", okudagram)
This lake was only mentioned in writing.