Index: src/landscape.cpp
===================================================================
--- src/landscape.cpp	(revision 27795)
+++ src/landscape.cpp	(working copy)
@@ -992,6 +992,32 @@
 }
 
 /**
+ * Check whether a river could (logically) flow into a lock.
+ * @param tile the middle tile of a lock.
+ * @return true iff the water can be flowing into a lock.
+ */
+static bool FlowsLock(TileIndex tile)
+{
+	DiagDirection dir = GetInclinedSlopeDirection(GetTileSlope(tile));
+	if (dir == INVALID_DIAGDIR) return false;
+
+	int delta = TileOffsByDiagDir(dir);
+
+	int height_tile;
+	if (DistanceFromEdge(tile - delta) <= 1 || !(GetTileSlope(tile - 2 * delta, &height_tile) == SLOPE_FLAT) && height_tile != 0 ||
+			DistanceFromEdge(tile - 2 * delta) <= 1 || !(GetTileSlope(tile - 2 * delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT)), &height_tile) == SLOPE_FLAT) && height_tile != 0 ||
+			!(GetTileSlope(tile - 2 * delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90LEFT)), &height_tile) == SLOPE_FLAT) && height_tile != 0 ||
+			DistanceFromEdge(tile - 2 * delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT))) <= 1 || !(GetTileSlope(tile - 3 * delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT)), &height_tile) == SLOPE_FLAT) && height_tile != 0 ||
+			!(GetTileSlope(tile - 3 * delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90LEFT)), &height_tile) == SLOPE_FLAT) && height_tile != 0) return false;
+
+	if (DistanceFromEdge(tile + delta) <= 1 || !IsTileFlat(tile + delta + delta) ||
+			DistanceFromEdge(tile + delta + delta) <= 1 || !IsTileFlat(tile + delta + delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT))) ||
+			!IsTileFlat(tile + delta + delta + TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90LEFT)))) return false;
+
+	return true;
+}
+
+/**
  * Check whether a river at begin could (logically) flow down to end.
  * @param begin The origin of the flow.
  * @param end The destination of the flow.
@@ -1008,9 +1034,9 @@
 
 	return heightEnd <= heightBegin &&
 			/* Slope either is inclined or flat; rivers don't support other slopes. */
-			(slopeEnd == SLOPE_FLAT || IsInclinedSlope(slopeEnd)) &&
+			(slopeEnd == SLOPE_FLAT || (IsInclinedSlope(slopeEnd) && FlowsLock(end))) &&
 			/* Slope continues, then it must be lower... or either end must be flat. */
-			((slopeEnd == slopeBegin && heightEnd < heightBegin) || slopeEnd == SLOPE_FLAT || slopeBegin == SLOPE_FLAT);
+			((slopeEnd == slopeBegin && heightEnd < heightBegin) || slopeEnd == SLOPE_FLAT || (slopeBegin == SLOPE_FLAT && GetTileMaxZ(end) == heightBegin));
 }
 
 /* AyStar callback for checking whether we reached our destination. */
@@ -1056,6 +1082,32 @@
 			MakeRiver(tile, Random());
 			/* Remove desert directly around the river tile. */
 			CircularTileSearch(&tile, 5, RiverModifyDesertZone, NULL);
+
+			/* Connect the water if a lock would be build on the inclined slope */
+			Slope slope = GetTileSlope(path->node.tile);
+			if (IsInclinedSlope(slope)) {
+				DiagDirection dir = GetInclinedSlopeDirection(slope);
+				int delta_mid = TileOffsByDiagDir(dir);
+				int delta     = TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT));
+				TileIndex tile_upper = path->node.tile + 2 * delta_mid;
+				TileIndex tile_upper_right = tile_upper + delta;
+				TileIndex tile_upper_right_far = tile_upper_right + delta_mid;
+				TileIndex tile_upper_left = tile_upper - delta;
+				TileIndex tile_upper_left_far = tile_upper_left + delta_mid;
+				TileIndex tile_lower = path->node.tile - 2 * delta_mid;
+				TileIndex tile_lower_right = tile_lower + delta;
+				TileIndex tile_lower_right_far = tile_lower_right - delta_mid;
+				TileIndex tile_lower_left = tile_lower - delta;
+				TileIndex tile_lower_left_far = tile_lower_left - delta_mid;
+				TileIndex tiles[] = {tile_upper, tile_upper_right, tile_upper_right_far, tile_upper_left, tile_upper_left_far, tile_lower, tile_lower_right, tile_lower_right_far, tile_lower_left, tile_lower_left_far};
+				for (int i = 0; i < lengthof(tiles); i++) {
+					if (!IsWaterTile(tiles[i]) && IsTileFlat(tiles[i])) {
+						MakeRiver(tiles[i], Random());
+						/* Remove desert directly around the river tile. */
+						CircularTileSearch(&tiles[i], 5, RiverModifyDesertZone, NULL);
+					}
+				}
+			}
 		}
 	}
 }