--- a/water_cmd.c	Sat Jun 03 12:53:29 2006 +0000
+++ b/water_cmd.c	Sat Jun 03 15:10:39 2006 +0000
@@ -148,7 +148,7 @@
 	}
 
 	if (flags & DC_EXEC) {
-		MakeLock(tile, dir);
+		MakeLock(tile, _current_player, dir);
 		MarkTileDirtyByTile(tile);
 		MarkTileDirtyByTile(tile - delta);
 		MarkTileDirtyByTile(tile + delta);
@@ -161,6 +161,8 @@
 {
 	TileIndexDiff delta = TileOffsByDir(GetLockDirection(tile));
 
+	if (!CheckTileOwnership(tile)) return CMD_ERROR;
+
 	// make sure no vehicle is on the tile.
 	if (!EnsureNoVehicle(tile) || !EnsureNoVehicle(tile + delta) || !EnsureNoVehicle(tile - delta))
 		return CMD_ERROR;
@@ -249,7 +251,11 @@
 		cost += ret;
 
 		if (flags & DC_EXEC) {
-			MakeWater(tile);
+			if (TileHeight(tile) == 0) {
+				MakeWater(tile);
+			} else {
+				MakeCanal(tile, _current_player);
+			}
 			MarkTileDirtyByTile(tile);
 			MarkTilesAroundDirty(tile);
 		}
@@ -279,6 +285,8 @@
 				return_cmd_error(STR_0002_TOO_CLOSE_TO_EDGE_OF_MAP);
 			}
 
+			if (GetTileOwner(tile) != OWNER_WATER && !CheckTileOwnership(tile)) return CMD_ERROR;
+
 			if (flags & DC_EXEC) DoClearSquare(tile);
 			return _price.clear_water;
 

--- a/water_map.h	Sat Jun 03 12:53:29 2006 +0000
+++ b/water_map.h	Sat Jun 03 15:10:39 2006 +0000
@@ -95,6 +95,16 @@
 	_m[t].m5 = 1;
 }
 
+static inline void MakeCanal(TileIndex t, Owner o)
+{
+	SetTileType(t, MP_WATER);
+	SetTileOwner(t, o);
+	_m[t].m2 = 0;
+	_m[t].m3 = 0;
+	_m[t].m4 = 0;
+	_m[t].m5 = 0;
+}
+
 static inline void MakeShipDepot(TileIndex t, Owner o, DepotPart base, Axis a)
 {
 	SetTileType(t, MP_WATER);
@@ -105,23 +115,23 @@
 	_m[t].m5 = base + a * 2;
 }
 
-static inline void MakeLockTile(TileIndex t, byte section)
+static inline void MakeLockTile(TileIndex t, Owner o, byte section)
 {
 	SetTileType(t, MP_WATER);
-	SetTileOwner(t, OWNER_WATER);
+	SetTileOwner(t, o);
 	_m[t].m2 = 0;
 	_m[t].m3 = 0;
 	_m[t].m4 = 0;
 	_m[t].m5 = section;
 }
 
-static inline void MakeLock(TileIndex t, DiagDirection d)
+static inline void MakeLock(TileIndex t, Owner o, DiagDirection d)
 {
 	TileIndexDiff delta = TileOffsByDir(d);
 
-	MakeLockTile(t, LOCK_MIDDLE + d);
-	MakeLockTile(t - delta, LOCK_LOWER + d);
-	MakeLockTile(t + delta, LOCK_UPPER + d);
+	MakeLockTile(t, o, LOCK_MIDDLE + d);
+	MakeLockTile(t - delta, o, LOCK_LOWER + d);
+	MakeLockTile(t + delta, o, LOCK_UPPER + d);
 }
 
 #endif