Its swimming muscles are weak, so it is easily washed away by currents. In places where water pools, you can see many MAGIKARP deposited there by flow.
(From Bulbapedia) Magikarp is a medium-sized fish Pokémon with large, heavy reddish-orange scales. It has large, vacant eyes and pink lips. Its pectoral and tail fins are white, but it has a stiff, three-peaked fin on its back and stomach that are both yellow. It also has long barbels.
The barbels on a female Magikarp are white, while male Magikarp have yellow barbels.
Prior to version 1.0.2, nuclear Magikarp had the same sprite as regular Magikarp. This did not affect its Water/Nuclear typing or other nuclear attributes.
(From Bulbapedia) Magikarp is based on a legend about how carp that leapt over the Dragon Gate would become dragons. Several waterfalls and cataracts in China are believed to be the location of the Dragon Gate. This legend is an allegory of the drive and efforts needed to overcome obstacles. Magikarp may also be based on Asian carp, which are easily frightened by disturbances in water and can jump 8–10 feet (2.5–3 m) in the air.
(From Bulbapedia) Magikarp's name is a combination of magic and carp, possibly mocking the Magikarp as a species, as someone with 'magic' powers is generally thought to be quite powerful, which Magikarp is not (though carp are said to be able to transform into dragons, which is magical in its own way).