diff --git a/src/dock_gui.cpp b/src/dock_gui.cpp
index f0e7130b92..bf446fadf3 100644
--- a/src/dock_gui.cpp
+++ b/src/dock_gui.cpp
@@ -162,7 +162,7 @@ struct BuildDocksToolbarWindow : Window {
 
 			case WID_DT_RIVER: // Build river button (in scenario editor)
 				if (_game_mode != GM_EDITOR && !_settings_game.construction.enable_build_river) return;
-				HandlePlacePushButton(this, WID_DT_RIVER, SPR_CURSOR_RIVER, HT_RECT);
+				HandlePlacePushButton(this, WID_DT_RIVER, SPR_CURSOR_RIVER, _game_mode == GM_EDITOR ? HT_RECT | HT_DIAGONAL : HT_RECT);
 				break;
 
 			case WID_DT_BUILD_AQUEDUCT: // Build aqueduct button
@@ -212,7 +212,7 @@ struct BuildDocksToolbarWindow : Window {
 				break;
 
 			case WID_DT_RIVER: // Build river button (in scenario editor)
-				VpStartPlaceSizing(tile, VPM_X_AND_Y, DDSP_CREATE_RIVER);
+				VpStartPlaceSizing(tile, (_game_mode == GM_EDITOR) ? VPM_X_AND_Y : VPM_X_OR_Y, DDSP_CREATE_RIVER);
 				break;
 
 			case WID_DT_BUILD_AQUEDUCT: // Build aqueduct button
@@ -239,7 +239,7 @@ struct BuildDocksToolbarWindow : Window {
 					DoCommandP(end_tile, start_tile, (_game_mode == GM_EDITOR && _ctrl_pressed) ? WATER_CLASS_SEA : WATER_CLASS_CANAL, CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_BUILD_CANALS), CcPlaySound_SPLAT_WATER);
 					break;
 				case DDSP_CREATE_RIVER:
-					DoCommandP(end_tile, start_tile, WATER_CLASS_RIVER, CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_PLACE_RIVERS), CcPlaySound_SPLAT_WATER);
+					DoCommandP(end_tile, start_tile, WATER_CLASS_RIVER | (_ctrl_pressed ? 1 << 2 : 0), CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_PLACE_RIVERS), CcPlaySound_SPLAT_WATER);
 					break;
 
 				default: break;
diff --git a/src/lang/english.txt b/src/lang/english.txt
index d1953b3aaf..e7553de198 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -2941,7 +2941,7 @@ STR_WATERWAYS_TOOLBAR_BUILD_DOCK_TOOLTIP                        :{BLACK}Build sh
 STR_WATERWAYS_TOOLBAR_BUOY_TOOLTIP                              :{BLACK}Place a buoy which can be used as a waypoint. Shift toggles building/showing cost estimate
 STR_WATERWAYS_TOOLBAR_BUILD_AQUEDUCT_TOOLTIP                    :{BLACK}Build aqueduct. Shift toggles building/showing cost estimate
 STR_WATERWAYS_TOOLBAR_CREATE_LAKE_TOOLTIP                       :{BLACK}Define water area.{}Make a canal, unless Ctrl is held down at sea level, when it will flood the surroundings instead
-STR_WATERWAYS_TOOLBAR_CREATE_RIVER_TOOLTIP                      :{BLACK}Place rivers
+STR_WATERWAYS_TOOLBAR_CREATE_RIVER_TOOLTIP                      :{BLACK}Place rivers. Ctrl selects the area diagonally.
 
 # Ship depot construction window
 STR_DEPOT_BUILD_SHIP_CAPTION                                    :{WHITE}Ship Depot Orientation
diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index ff148b8a23..d7199d5962 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -387,7 +387,9 @@ bool RiverModifyDesertZone(TileIndex tile, void *)
  * @param tile end tile of stretch-dragging
  * @param flags type of operation
  * @param p1 start tile of stretch-dragging
- * @param p2 waterclass to build. sea and river can only be built in scenario editor, unless enable_build_river is enabled
+ * @param p2 various bitstuffed data
+ *  bits  0-1: waterclass to build. sea and river can only be built in scenario editor, unless enable_build_river is enabled
+ *  bit     2: Whether to use the Orthogonal (0) or Diagonal (1) iterator.
  * @param text unused
  * @return the cost of this operation or an error
  */
@@ -398,6 +400,7 @@ CommandCost CmdBuildCanal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 	/* Outside of the editor you can only build canals, not oceans */
 	if (_game_mode != GM_EDITOR) {
+		if (HasBit(p2, 2)) return CMD_ERROR;
 		if (wc == WATER_CLASS_RIVER) {
 			if (!_settings_game.construction.enable_build_river) return CMD_ERROR;
 		} else if (wc != WATER_CLASS_CANAL) {
@@ -405,13 +408,17 @@ CommandCost CmdBuildCanal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 		}
 	}
 
-	TileArea ta(tile, p1);
-
 	/* Outside the editor you can only drag canals, and not areas */
-	if (_game_mode != GM_EDITOR && ta.w != 1 && ta.h != 1) return CMD_ERROR;
+	if (_game_mode != GM_EDITOR) {
+		TileArea ta(tile, p1);
+		if (ta.w != 1 && ta.h != 1) return CMD_ERROR;
+	}
 
 	CommandCost cost(EXPENSES_CONSTRUCTION);
-	TILE_AREA_LOOP(tile, ta) {
+
+	TileIterator *iter = HasBit(p2, 2) ? (TileIterator *)new DiagonalTileIterator(tile, p1) : new OrthogonalTileIterator(tile, p1);
+	for (; *iter != INVALID_TILE; ++(*iter)) {
+		TileIndex tile = *iter;
 		CommandCost ret;
 
 		Slope slope = GetTileSlope(tile);