I read that it does so every 1000 years or so? Is all the work they’ve been doing with spillways and other stuff over the last 100 years been about trying to stop this, or am I confused?
Basically, yes. The Mississippi, if left to its own devices, would flow into the Atchafalaya River, abandoning New Orleans for a more direct route to the sea.
One thing that has interfered with the route has been the extensive series of levees that have been built over the years. There are many who think that that enterprise has been massively counterproductive, but the fact is that in addition to man-made changes, climates change, conditions change, land changes, and, yes, rivers change their courses. It’s been going on for approximately 1.5 gazillion years. Just not on a regular 1000 year cycle, as the OP seems to think.
The lower Mississippi has wandered around all over the place throughout history. It isn’t a small area. We are talking about significant parts at least two states. It would change course on its own again but we decided to try and lock it into its current channel. If you have never seen the earthworks that make that happen, it is a sight to behold. I used to live next to the river in New Orleans and I could walk out of my door and see the tops of giant ships cruising by if I looked up. Generally, if you have to look up to see ships passing by, that is a bad sign but that is what people decided to do about the problem a long time ago. It will change course again at some point but hopefully not this month.
Similar and recent thread.
Evolution of the Mississipi River Delta in Wikipedia. It might be noted that the course of the Mississippi changes on a yearly and almost on a daily basis, as it erodes away banks to crfeate and then intercut meanders.
If you look at history before the major construction of levees on the lower Mississippi, it changed courses and took big diversion a LOT more often than every 1,000 years.
Now south of Cairo, Illinois the Mississippi, is basically a canal of storts, maintaining it’s course through artificial structures.
Left to its own devices, the river has the potential to change during the annual spring flood every year.
In the recorded history of the Mississippi River, which only goes back a few hundred years, it’s rerouted hundreds of times. It’s only in the past century that they’ve been able to control the river with spillways and levees and keep it flowing the way it does now.
Follow the Mississippi north from New Orleans on Google maps and see all of the loops and lakes and false rivers that have formed over the years.
Just north of Memphis, there are exclaves of Tennessee and Arkansas on the wrong side of the river every few miles, all due to rerouting of the river.
There’s a set of rather pretty maps created in the '40’s which show the meandering of the River over time. This link shows one map, you can download the others (the files are rather large). I’d love to print them all full-size and frame them.