diff --git a/features/Upscaling/Shaders/Upscaling/UnderwaterMaskUpscalePS.hlsl b/features/Upscaling/Shaders/Upscaling/UnderwaterMaskUpscalePS.hlsl
index 66dfd559be..213ccd6931 100644
--- a/features/Upscaling/Shaders/Upscaling/UnderwaterMaskUpscalePS.hlsl
+++ b/features/Upscaling/Shaders/Upscaling/UnderwaterMaskUpscalePS.hlsl
@@ -63,6 +63,15 @@ PS_OUTPUT main(PS_INPUT input)
 	// itself, which always maps to the center tile (12).
 	float waterHeight = SharedData::GetWaterData(float3(0, 0, 0), eyeIndex).w;
 
+	// Tile sentinel: try TESWaterSystem fallback. WaterSystemHeight is valid only when
+	// playerUnderwater == true (fully submerged); it is stored eye-0 camera-relative so
+	// the same per-eye correction as GetWaterData applies.
+	if (waterHeight <= WATER_HEIGHT_NO_TILE_SENTINEL) {
+		float sysHeight = SharedData::WaterSystemHeight;
+		if (sysHeight > WATER_HEIGHT_NO_TILE_SENTINEL)
+			waterHeight = sysHeight + FrameBuffer::CameraPosAdjust[0].z - FrameBuffer::CameraPosAdjust[eyeIndex].z;
+	}
+
 	// GetWaterData returns INT_MIN (~-2.147e9) when the tile is outside the 5x5 grid.
 	if (waterHeight > WATER_HEIGHT_NO_TILE_SENTINEL) {
 		// Unpack from side-by-side stereo layout to per-eye UV [0, 1]
@@ -112,9 +121,10 @@ PS_OUTPUT main(PS_INPUT input)
 		}
 		return psout;
 	}
-	// No water tile in range: fall through to the standard sampler path.
+	// No water tile or system height available: fall through to the standard sampler path.
 	// The left-eye result from the vanilla mask is still accurate here; the right-eye
-	// will be approximate, but in the absence of nearby water the visual impact is nil.
+	// will be approximate, but both sources failing implies no nearby water so the
+	// visual impact is nil.
 #	endif
 
 	// Upscale using linear sampling with jitter-corrected coordinates
diff --git a/package/Shaders/Common/SharedData.hlsli b/package/Shaders/Common/SharedData.hlsli
index 767068f6df..ed40111591 100644
--- a/package/Shaders/Common/SharedData.hlsli
+++ b/package/Shaders/Common/SharedData.hlsli
@@ -20,11 +20,11 @@ namespace SharedData
 		float Timer;
 		uint FrameCount;
 		uint FrameCountAlwaysActive;
-		bool InInterior;  // If the area lacks a directional shadow light e.g. the sun or moon
-		bool InMapMenu;   // If the world/local map is open (note that the renderer is still deferred here)
-		bool HideSky;     // HideSky flag in WorldSpace, e.g. Blackreach
-		float MipBias;    // Offset to mip level for TAA sharpness
-		float pad0;
+		bool InInterior;          // If the area lacks a directional shadow light e.g. the sun or moon
+		bool InMapMenu;           // If the world/local map is open (note that the renderer is still deferred here)
+		bool HideSky;             // HideSky flag in WorldSpace, e.g. Blackreach
+		float MipBias;            // Offset to mip level for TAA sharpness
+		float WaterSystemHeight;  // TES::GetWaterHeight at eye-0 in camera-relative Z; -FLT_MAX when no water body found (VR only)
 		float4 AmbientSHR;
 		float4 AmbientSHG;
 		float4 AmbientSHB;
diff --git a/src/State.cpp b/src/State.cpp
index 4892da9424..04db5dd2ae 100644
--- a/src/State.cpp
+++ b/src/State.cpp
@@ -856,6 +856,24 @@ void State::UpdateSharedData([[maybe_unused]] bool a_inWorld, [[maybe_unused]] b
 			}
 		}
 
+		// Fallback water height for the VR analytical mask when tile 12 returns the sentinel.
+		// Uses player->GetWaterHeight() (reads relevantWaterHeight from LOADED_REF_DATA) gated by
+		// underwaterCount > 0 so it is only set when the player is actually in a water body.
+		// Covers both interior water (where TES::GetWaterHeight returns -NI_INFINITY) and exterior
+		// partial submersion.  Stored as eye-0 camera-relative Z to match WaterData[].w.
+		data.WaterSystemHeight = -RE::NI_INFINITY;
+		if (globals::game::isVR) {
+			if (auto player = globals::game::player) {
+				if (player->loadedData && player->loadedData->underwaterCount > 0) {
+					float worldHeight = player->GetWaterHeight();
+					if (worldHeight > -RE::NI_INFINITY) {
+						auto eye0Pos = Util::GetEyePosition(0);
+						data.WaterSystemHeight = worldHeight - eye0Pos.z;
+					}
+				}
+			}
+		}
+
 		data.InInterior = Util::IsInterior();
 
 		if (globals::game::sky)
diff --git a/src/State.h b/src/State.h
index 3d9ae141ec..ad2658888b 100644
--- a/src/State.h
+++ b/src/State.h
@@ -218,7 +218,7 @@ class State
 		uint InMapMenu;
 		uint HideSky;
 		float MipBias;
-		float pad0;  // unused; must match SharedData.hlsli cbuffer (AmbientSHR 16-byte alignment)
+		float WaterSystemHeight;  // TES::GetWaterHeight at eye-0 in camera-relative Z; -NI_INFINITY when no water body found (VR only)
 		float4 AmbientSHR;
 		float4 AmbientSHG;
 		float4 AmbientSHB;
diff --git a/src/Utils/Game.cpp b/src/Utils/Game.cpp
index 31900f417c..464bc863d0 100644
--- a/src/Utils/Game.cpp
+++ b/src/Utils/Game.cpp
@@ -84,7 +84,9 @@ namespace Util
 						data.z *= color.blue;
 					}
 
-					data.w = cell->GetExteriorWaterHeight() - position.z;
+					float cellWaterHeight;
+					if (cell->GetWaterHeight(position, cellWaterHeight))
+						data.w = cellWaterHeight - position.z;
 
 					return data;
 				}