From (Season 2 Episode 4) “Two Cars in Every Garage and Three Eyes on Every Fish”
After Bart catches a three-eyed fish in a river downstream of the Springfield Nuclear Power Plant, the Plant is inspected and found to have 342 violations, which would cost $56 million to rectify. In order to prevent his Plant from being shut down, Mr. Burns decides to run for Governor. After a hard campaign which sees Burns rise from being universally despised to running neck and neck with incumbent Mary Bailey, it is decided that Burns will have dinner with a random employee the night before the election. Homer is chosen, much to Marge’s chagrin. Marge serves the three eyed fish to Burns for dinner, who can not eat it and as a result, loses the election.