Make Minecraft River wider?

I want to make my river wider in Minecraft, but the flow then breaks in the middle of the river by 90 °, resulting in a kind of T. How can I prevent this?

You have to fill it with buckets of water so that there's at least a whole water source around the river then everything is filled with knowledge from minecraft wiki

I didn't quite understand what you mean, but if I've interpreted it correctly: Simply fill the second layer under water with a constant block, place water on top and then remove the blocks again. Then there should be no more "currents".

Best wishes