Historically, the Everglades used to cover most of South Florida, stretching from present day Orlando all the way south to the Florida Keys. Water from the Kissimmee River would fill Lake Okeechobee and then flow south into the River of Grass. But sadly, this is no longer what the Everglades looks like.
For about the past 7000 years, rain has fallen on the Kissimmee basin and flowed south into the lake. Humans have changed the timing of inflows, and maybe increased the volume a bit, and agriculture has certainly polluted that water, but it flows more or less the same today. But south of the lake, nothing works at all like it did. The Everglades Agricultural Area (EAA) is now the only source of water for the Everglades, and it’s polluted. So, the focus is on repairing what has been profoundly modified, and putting it back into some semblance of how it used to work.