Before May 27, 2016, the water parks could become extremely crowded during Easter time as long as the weather was warm, to the point that they could sometimes close to new guests for two to three hours in late morning to early afternoon due to over-capacity. At that time the bus route had the resort's AK bus stopping at Blizzard Brach and its Studios bus at Typhoon Lagoon. Then some MBA Suit decided that the better bus schedule for the waterparks was to have everyone go to Disney Springs first and switch there to Typhoon Lagoon or to AK first and switch to Blizzard Beach, with the result that traveling to or from a waterpark typically became an hour or longer trip, and guests got to stand at the bus station at AK or Disney Springs much of the time waiting for their intended bus in their swimsuits. The result was that crowds for the water parks became lighter, and I am sure that the MBA Suit who came up with the new bus route was shocked, just shocked, that many would avoid the water parks with that double bus trip.
Be aware that effective March 17, 2019, Disney finally came to its senses and the double bus route was rightly put to death, and it has now returned to something similar to what existed before, see
https://www.wdwinfo.com/news-stories/new-bus-routes-for-walt-disney-world-water-parks-2/ As a result, the waterparks could become very crowded again during Easter time, although it may take a while before most realize that the lousy double bus schedule has been replaced.
Also, as long as weather is good, the resort pools will also be very crowded, and if you actually want a place to sit down, you may need to claim it early in the morning.