I ran my compile log through the checker, it came out with something very weird: *** Error: Skybox vtf files for skybox/sky_well_01 weren't compiled with the same size texture and/or same flags! Can't load skybox file skybox/sky_well_01 to build the default cubemap! The advice given was: You have entered a skybox texture which doesn't seem to be valid. Make sure you don't specify the last three letter (_UP, _DN, etc) of any skybox texture you use. You may also need to fix your vmt files if they are broken. It may also be caused by compiling a non-HDR skybox texture. But this was using one of the pre-made skyboxes (the one used on well) so there can't be an error with the file-naming. And the skybox is HDR as well, so no problem there. Also, I don't know if this is related or not, but there are no cubemaps in my map, yet water still reflects things around it.