Starting today at 1 P.M. PDT, you'll be more likely to encounter Magikarp, Squirtle, Totodile, and their evolutions all around the world. Additionally, when you're out exploring areas where Water-type Pokémon more commonly appear, you'll have a greater chance to encounter several of the Water-type Pokémon originally discovered in the Johto region, and maybe... you might even encounter Lapras.
This event lines up well with an adjustment to the game's 7-Day Streak mechanic, promising an evolution item drop every time you complete a streak instead of just a random chance. The event lasts exactly seven days, which means if you are an active player every day until the 29th you'll not only have an arsenal of new water-type creatures to battle with but you'll also have a decent chance of evolving one into something even better.
Now get out there and catch yourself a Lapras. You deserve it.