diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -301,7 +301,7 @@ static CommandCost DoBuildLock(TileIndex
 	if (ret.Failed()) return ret;
 
 	/* middle tile */
-	WaterClass wc_middle = IsWaterTile(tile) ? GetWaterClass(tile) : WATER_CLASS_CANAL;
+	WaterClass wc_middle = HasTileWaterGround(tile) ? GetWaterClass(tile) : WATER_CLASS_CANAL;
 	ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
 	if (ret.Failed()) return ret;
 	cost.AddCost(ret);