It's all happening in Pokémon Go. Developer Niantic announced yesterday that an unexpected Water Festival would be kicking off at 8pm UK time, and it lasts until 8pm on the 29th. During the festival, you've got more chance of running into water 'mon like Magikarp, Squirtle, Totodile and so on – and you've got a better chance of finding Gen 2 water species in watery areas too.
At the same time, PoGo users started finding shiny Pokémon in the wild, including this Reddit user's Magikarp:
Shortly afterwards, Twitter user IsolinoSA reported that evolving a shiny Magikarp resulted in a red Gyarados:
— Aisailand (@IsolinoSA) March 22, 2017
In addition to all this excitement is, in my opinion, the most exciting new feature: a free Magikarp hat for your avatar that makes it look like you're being eaten by a fish. Here's mine lookin' fancy:
You can get it from the Style options under Hats. Hopefully they'll release one in real life too, but in the meantime there's always Etsy.