/* Sloped rivers need water both upstream and downstream. */

	if (IsInclinedSlope(cur_slope)) {

		DiagDirection slope_direction = GetInclinedSlopeDirection(cur_slope);

		TileIndex upstream_tile = TileAddByDiagDir(tile, slope_direction);

		TileIndex downstream_tile = TileAddByDiagDir(tile, ReverseDiagDir(slope_direction));

		/* Don't look outside the map. */

		if (!IsValidTile(upstream_tile) || !IsValidTile(downstream_tile)) return false;

		/* Downstream might be new ocean created by our terraforming, and it hasn't flooded yet. */

		bool downstream_is_ocean = GetTileZ(downstream_tile) == 0 && (GetTileSlope(downstream_tile) == SLOPE_FLAT || IsSlopeWithOneCornerRaised(GetTileSlope(downstream_tile)));

		/* If downstream is dry, flat, and not ocean, try making it a river tile. */

		if (!IsWaterTile(downstream_tile) && !downstream_is_ocean) {

			/* If the tile upstream isn't flat, don't bother. */

			if (GetTileSlope(downstream_tile) != SLOPE_FLAT) return false;

			MakeRiver(downstream_tile, Random());

		}

		/* If upstream is dry and flat, try making it a river tile. */

		if (!IsWaterTile(upstream_tile)) {

			/* If the tile upstream isn't flat, don't bother. */

			if (GetTileSlope(upstream_tile) != SLOPE_FLAT) return false;

			MakeRiver(upstream_tile, Random());

		}

	}