A university study from 2018 has revealed that Wailord needs to eat a lot of other Pokémon just to make sure it doesn't float away.
Wailord is a big Pokemon. In fact, it's canonically the biggest organism in the entire Pokemon universe. Wailord is so big that all it needs to do to knock you out is make a big splash. Its size has been the subject of many memes and is the major reason behind its popularity amongst the Pokemon community. You'd think that something that makes a building look small in comparison would also weigh a considerable amount. You'd be wrong.
Due to an apparent typo in Wailord's Pokedex entry when it was first introduced, Wailord only weighs 398kg. In relation to its size, that means Wailord is less dense than air and will literally float into space if it doesn't increase its mass. This interesting tidbit was discovered in an actual university research paper by William Farmer from the University of Leicester in the UK.
He goes on to explain what Wailord has to do in order to stay in the water. To increase its mass enough to stop itself from floating into the cold emptiness of space, Wailord has to eat a minimum of 55.36kg of food. This amount would stop Wailord from floating away and keep it in the water where it belongs. Good news if you're a Wailord, but very bad news if you're a Wishiwashi or a Luvdisc.
According to Wailord's Bulbapedia entry, its diet mainly consists of schools of Wishwashi and the occasional Luvdisc, Pokemon that are considerably smaller than Wailord itself. After a whole lot of maths and equations, (trust me on this) it works out that Wailord needs to eat a total of either 178 Wishiwashi, 7 Luvdisc, or a combination of the two. This amount of food allows Wailord to sit comfortably in the ocean but also lets it dive 3000m below the sea, something which Wailord's Pokedex entry also states it can do.
If you take anything away from this, let it be the fact that Wailord is not as innocent as it seems. Whenever you see a Wailord on the horizon in Pokemon Sword and Shield, just casually floating on the ocean minding its own business, be aware that it's likely eaten hundreds of Pokemon to be able to do that.