Odd bumps on water surfaces in Cesium World Terrain UE5

Hi all, I’m very new to Cesium, and still kind of new to Unreal. Very impressed with the plugin and ease of use so far.

I’ve got it set up in a UE5 level with great results, but I’m just hitting an issue with odd bumps appearing on water surfaces in the terrain mesh.

The bumps don’t appear in open ocean, but there’s lots in rivers, lakes, and the coast. The area I’m looking at is Melbourne, Australia.

It’s almost like the terrain contour data for waterways is being inverted? A lake that’s supposed to be 10m deep, is instead a 10m tall hill, for example.

Is this a limitation of the source data that Cesium is reading? Or is there a setting I’ve messed up?