Its 1 massive damn!
On this post we want to show you this dam built by kingyatesy on which there is a structure to keep the water from flowing over a city.
We personally think this is a little small compared to a real life dam but the idea is to give you the inspiration and basic steps to take and build your own, in this case it will be replicating the same structure multiple times until you reach your desired size.
Remember to add this dam into the outside of a city or in a valley which is where they are usually located. Also, if you can build it in a way that is also an Hydropower source then it will pair perfectly with other renewable energy builds you can add to your world.