diff -r e7a6bbce5400 -r 7f8b5c11bea6 src/tunnelbridge_cmd.cpp
--- a/src/tunnelbridge_cmd.cpp	Sat Jan 19 14:00:04 2008 +0000
+++ b/src/tunnelbridge_cmd.cpp	Sat Jan 19 17:00:54 2008 +0000
@@ -376,7 +376,7 @@
 		switch (GetTileType(tile)) {
 			case MP_WATER:
 				if (!EnsureNoVehicleOnGround(tile)) return_cmd_error(STR_980E_SHIP_IN_THE_WAY);
-				if (!IsWater(tile) && !IsCoast(tile)) goto not_valid_below;
+				if (!IsWater(tile) && !IsCoast(tile) && !IsRiver(tile)) goto not_valid_below;
 				break;
 
 			case MP_RAILWAY: