when you generate a world,sometimes the water has a invisible "wall" in the desert biome.
Just look at the picture below.
PD: I don't know if this bug is fixed or in fix working,but this bug is from alpha version maybe.
Thanks for reading this report
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This is not a bug, it is just the generation.
Update the water and it should work.

This is the "normal" Minecraft mechanics
Why was this marked as resolved? Just because this bug has always been in minecraft doesnt make it any less of a bug! I highly doubt that mojang intentionally programmed their world generator to create random walls of still water. Furthermore I dont think this would be that hard to fix, all they would have to do is send block updates to the water-source blocks that are along the edge of a body of water. In fact, the updates probably only have to go to the bodies of water that are adjacent to sand/gravel blocks.