This painful infection causes bleeding from the eyes and eventually blinds the victim.

A beast or humanoid that drinks water tainted by sight rot must succeed on a DC 15 Constitution saving throw or become infected. One day after infection, the creature's vision starts to become blurry. The creature takes a -1 penalty to attack rolls and ability checks that rely on sight. At the end of each long rest after the symptoms appear, the penalty worsens by 1. When it reaches -5, the victim is blinded until its sight is restored by magic such as Lesser Restoration or Heal.

Sight rot can be cured using a rare flower called Eyebright, which grows in some swamps. Given an hour, a character who has proficiency with an herbalism kit can turn the flower into one dose of ointment. Applied to the eyes before a long rest, one dose of it prevents the disease from worsening after that rest. After three doses, the ointment cures the disease entirely.