apps/web/src/widgets/map3d/Map3D.tsx

@@ -218,6 +218,10 @@ function injectOceanBathymetryLayers(style: StyleSpecification, maptilerKey: str
     type: "fill",
     source: oceanSourceId,
     "source-layer": "contour",
+    // Very low zoom tiles can contain extremely complex polygons (coastline/detail),
+    // which may exceed MapLibre's per-segment 16-bit vertex limit and render incorrectly.
+    // We keep the fill starting at a more reasonable zoom.
+    minzoom: 4,
     paint: {
       // Dark-mode friendly palette (shallow = slightly brighter; deep = near-black).
       "fill-color": bathyFillColor,