Index: src/town_cmd.cpp
===================================================================
--- src/town_cmd.cpp	(revision 27632)
+++ src/town_cmd.cpp	(working copy)
@@ -871,6 +871,9 @@
 	/* Prevent towns from building roads under bridges along the bridge. Looks silly. */
 	if (IsBridgeAbove(tile) && GetBridgeAxis(tile) == DiagDirToAxis(dir)) return false;
 
+	/* Prevent towns from building roads where ships can traverse */
+	if ((TrackStatusToTrackBits(GetTileTrackStatus(tile, TRANSPORT_WATER, 0)) & TRACK_BIT_ALL) != TRACK_BIT_NONE) return false;
+
 	/* Check if there already is a road at this point? */
 	if (GetTownRoadBits(tile) == ROAD_NONE) {
 		/* No, try if we are able to build a road piece there.
@@ -1103,6 +1106,9 @@
 	/* no water tiles in between? */
 	if (bridge_length == 1) return false;
 
+	/* Don't build the bridge if the bridge head at the destination is traversable by ships */
+	if ((TrackStatusToTrackBits(GetTileTrackStatus(bridge_tile, TRANSPORT_WATER, 0)) & TRACK_BIT_ALL) != TRACK_BIT_NONE) return false;
+
 	for (uint8 times = 0; times <= 22; times++) {
 		byte bridge_type = RandomRange(MAX_BRIDGES - 1);
 
@@ -1158,6 +1164,7 @@
 
 			case TL_3X3_GRID:
 			case TL_2X2_GRID:
+				if ((TrackStatusToTrackBits(GetTileTrackStatus(tile, TRANSPORT_WATER, 0)) & TRACK_BIT_ALL) != TRACK_BIT_NONE) return;
 				rcmd = GetTownRoadGridElement(t1, tile, target_dir);
 				if (rcmd == ROAD_NONE) return;
 				break;
@@ -2066,7 +2073,7 @@
 {
 	/* cannot build on these slopes... */
 	Slope slope = GetTileSlope(tile);
-	if ((noslope && slope != SLOPE_FLAT) || IsSteepSlope(slope)) return false;
+	if ((noslope && slope != SLOPE_FLAT) || IsSteepSlope(slope) || ((TrackStatusToTrackBits(GetTileTrackStatus(tile, TRANSPORT_WATER, 0)) & TRACK_BIT_ALL) != TRACK_BIT_NONE)) return false;
 
 	/* building under a bridge? */
 	if (IsBridgeAbove(tile)) return false;