The curse of the lake is a curse that will lead everyone that died on the lake or a body thrown in the lake to come back to life.
In Lakeview Cabin III, you can see the curse in action of you kill one of your caracter and throw it on the lake.
After a few minutes, your character will come back as a Zombie, wich add another, pretty weak, killer.
In Lakeview Cabin IV, inside one of the many secret room, you can find the Last Will wich says "I'm burning down the factory and cursing the lake you sought to protect.", showing that the writter of this page might be the cause of this curse.
Nothing about the lake is said in Lakeview Cabin V due the fact it takes place away from the lake.
The curse is one of the many things the space station studies.