TileIndex t2 = end + TileOffsByDiagDir(d);

			if (IsValidTile(t2) && !marks[t2] && FlowsDown(end, t2)) {

				marks[t2] = true;

				count++;

				queue.push_back(t2);

			}

		}

	} while (!queue.empty());

	if (found) {

		/* Flow further down hill. */

		found = FlowRiver(marks, spring, end);

		/* Maybe we can make a lake. Find the Nth of the considered tiles. */

		TileIndex lakeCenter = 0;

		for (int i = RandomRange(count - 1); i != 0; lakeCenter++) {

			if (marks[lakeCenter]) i--;

		}

		if (IsValidTile(lakeCenter) &&

				/* A river, or lake, can only be built on flat slopes. */

				GetTileSlope(lakeCenter, NULL) == SLOPE_FLAT &&

				/* We want the lake to be built at the height of the river. */

				TileHeight(begin) == TileHeight(lakeCenter) &&

				/* We don't want the lake at the entry of the valley. */