The pond band has near-zero variance (0.002) — perfectly uniform color, which means it's NOT water (water would have some noise variation from the bump/reflection). A perfectly uniform 0.42,0.37,0.30 is the PathMat or GroundMat flat color. The pond water isn't rendering there.

Let me check: is the pond water disc maybe COVERED by the ground? The ground is a grid with vertices — at the pond, the terrain dips, but the ground mesh between vertices is flat triangles. The water disc at z=0.25 — if the ground mesh at that point is ABOVE 0.25 (because of the dish shape), the water would be hidden. But we verified the ground near the pond center is at -0.6 to -1.2, below 0.25.

Wait — maybe the camera is seeing the pond area at such a shallow angle that the water disc (flat, thin) is edge-on and effectively invisible, and the ground behind/below shows. Let me check from the camera: what's the angle? The camera at (15.5,-15.5,5) looking at (-1.5,-1.5,2). The pond center (8,-7) — the view direction from camera to pond center is roughly (8-15.5, -7+15.5, 0.25-5) = (-7.5, 8.5, -4.75). The water normal is (0,0,1). The angle between view direction and water normal: cos = -4.75/sqrt(56+72+22.6)= -4.75/12.3 = -0.39 → angle ~113°. So we see the water at a fairly steep angle — it should be clearly visible.

Hmm. Let me check if maybe the water disc is being culled or the material renders transparent (fully transparent water with no refraction showing the ground below — and the ground below at the pond bottom is GroundMat (grass green), not this dirt color.

The uniform 0.42,0.37,0.30 — that's suspicious. Let me find which material has base color closest to this. PathMat mix of (0.42,0.34,0.24) and (0.27,0.21,0.14) → around 0.34,0.27,0.19. GroundMat: (0.30,0.42,0.19)/(0.13,0.22,0.09) → around 0.21,0.32,0.14 (greenish). The sampled 0.42,0.37,0.30 is lighter and neutral-warm.

Let me directly render with a debug pass: set the water to a bright red emission temporarily and see if it shows. Or use the viewport to check. Let me temporarily assign a bright red material to the pond and render.

import bpy, os, tempfile
import numpy as np

# temporary: make water bright red
mat = bpy.data.materials.get('WaterMat')
orig = mat.node_tree.nodes['Principled BSDF'].inputs['Base Color'].default_value
print('orig base color', orig)
mat.node_tree.nodes['Principled BSDF'].inputs['Base Color'].default_value = (1.0, 0.0, 0.0, 1.0)
mat.node_tree.nodes['Principled BSDF'].inputs['Transmission Weight'].default_value = 0.0
mat.node_tree.nodes['Principled BSDF'].inputs['Roughness'].default_value = 0.3

out = os.path.join(tempfile.gettempdir(), 'check_red.png')
bpy.context.scene.render.filepath = out
bpy.ops.render.render(write_still=True)
print('rendered', out, os.path.getsize(out))

p = out
img = bpy.data.images.load(p)
w, h = img.size
px = np.array(img.pixels[:], dtype=float).reshape((h, w, 4))[..., :3]
from mathutils import Vector
from bpy_extras.object_utils import world_to_camera_view
cam = bpy.data.objects['Camera']
scene = bpy.context.scene
for xyz, label in [((8,-7,0.25),'pond_center'), ((8,-3,0.25),'pond_north'), ((5,-5,0.25),'pond_west')]:
    v = world_to_camera_view(scene, cam, Vector(xyz))
    if 0 <= v.x <= 1 and 0 <= v.y <= 1:
        col = int(v.x*w); row = int((1-v.y)*h)
        print(label, (round(v.x,3), round(v.y,3)), 'rgb', px[row,col].round(3))
    else:
        print(label, 'off', (round(v.x,3), round(v.y,3)))
bpy.data.images.remove(img)


orig base color <bpy_float[4], NodeSocketColor.default_value>
rendered <home>\AppData\Local\Temp\check_red.png 2562799
pond_center (0.67, 0.197) rgb [0.424 0.373 0.302]
pond_north (0.881, 0.278) rgb [0.42  0.369 0.302]
pond_west (0.604, 0.303) rgb [0.62  0.561 0.478]