Index: src/water_cmd.cpp
===================================================================
--- src/water_cmd.cpp	(revision 27200)
+++ src/water_cmd.cpp	(working copy)
@@ -39,7 +39,7 @@
 #include "company_base.h"
 #include "company_gui.h"
 #include "newgrf_generic.h"
-
+#include "cheat_type.h"
 #include "table/strings.h"
 
 #include "safeguards.h"
@@ -470,6 +470,8 @@
 			if (flags & DC_NO_WATER) return_cmd_error(STR_ERROR_CAN_T_BUILD_ON_WATER);
 
 			Money base_cost = IsCanal(tile) ? _price[PR_CLEAR_CANAL] : _price[PR_CLEAR_WATER];
+			if (IsRiver(tile) && _game_mode == GM_NORMAL && !_cheats.magic_bulldozer.value) base_cost = 0;
+
 			/* Make sure freeform edges are allowed or it's not an edge tile. */
 			if (!_settings_game.construction.freeform_edges && (!IsInsideMM(TileX(tile), 1, MapMaxX() - 1) ||
 					!IsInsideMM(TileY(tile), 1, MapMaxY() - 1))) {
@@ -491,7 +493,9 @@
 					Company::Get(owner)->infrastructure.water--;
 					DirtyCompanyInfrastructureWindows(owner);
 				}
+				bool river = HasTileWaterClass(tile) && GetWaterClass(tile) == WATER_CLASS_RIVER;
 				DoClearSquare(tile);
+				if (river && _game_mode == GM_NORMAL && !_cheats.magic_bulldozer.value) MakeRiver(tile, Random());
 				MarkCanalsAndRiversAroundDirty(tile);
 			}
 
@@ -1314,6 +1318,7 @@
 	/* Canals can't be terraformed */
 	if (IsWaterTile(tile) && IsCanal(tile)) return_cmd_error(STR_ERROR_MUST_DEMOLISH_CANAL_FIRST);
 
+	if (IsWaterTile(tile) && IsRiver(tile)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
 	return DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
 }