About this "The Simpsons" episode:

The Simpsons - The Old Man and the Lisa is the 21st episode of season 8 and number 174 overall in the series.
In this episode Mr. Burns gets broke. He loses his fortune in a bad investment. He is not doing well alone and is committed to the Springfield Retirement Castle. Disgusted by his surroundings, he vows to get his fortune back. He then sees Lisa collecting recyclables and remembers her opposition towards him. He believes that the reason for losing his fortune was that he was surrounded by "yes men" and therefore asks Lisa to help him. Lisa introduces Burns to recycling and by collecting these he soon gets enough money to buy a recycling plant. In reality this recycling plant captures all aquatic life and grinds it into to all-purpose goo. Lisa is horrified, but Burns regains his fortune and buys back his power plant.