While we know that Disney had previously confirmed that they will finally reopen one of their waterparks to guests on March 7, 2021, they were not ready to name which of the parks this would be. That has changed this week, with the official announcement on the website confirming that Blizzard Beach will be the waterpark to open first on March 7, 2021.
It is also worth mentioning that before COVID impacted everything, Blizzard Beach was hard at work replacing the entire slide for the Summit Plummet attraction with new fiberglass slide pieces back in December 2019. So when you visit, be sure to check this one out, as the brand new slide should be as smooth as glass. After such a long extended closure, I would imagine that there may be other smaller refurbishments worth noting across the park when it opens as well.