Oh dear. Apparently the dam you started building on the river was too much for it. The added weight collapsed the river into a raging underground river running below it!
Fortunately, the area you started your dam at was already a low point and a tributary downstream is still supplying you with a little bit of water. Build slowly, build carefully.
Much of the usable flat land, as well as all your efforts before this, have been washed away. Try not to repeat this.
This is a medium to hard difficulty map, not recommended for beginners. Intended for normal difficulty, hard is not impossible but will be difficult.
NOTE: The water in the underground river may not behave like you would expect it to. This is a feature, not a bug.
NOTE: If you wish to interfere with the underground river's path, it really doesn't want you to. It WILL NOT react the way that you expect. You have been warned.
https://mod.io/g/timberborn/m/underground-river

