It a swimming pool located behind the Krusty Krab. It is a large-sized built-in pool with no water in it. It costs $1.00 to swim, as the pink clam-shaped sign says.
Role in episode
Mr. Krabs builds the Krusty Pool to increase his profits. To allow him to open the pool year-round, he uses a parked boatmobile to pump carbon dioxide into the air, thus creating an "endless summer."
When SpongeBob tries to speed up the process by using many boats at once, a mob of citizens are seen running towards the Krusty Krab. Mr. Krabs thinks they are going to the pool and orders SpongeBob to fill it. However, they literally run right over Krabs, and Patrick explains to him that they are moving north, not being able to live in the new climate because it is too hot.
Since there is no line to go into the pool, SpongeBob becomes excited and attempts to cannonball. However, the water quickly evaporates and SpongeBob lands in the empty concrete pool, injuring himself in the process.