/* lower tile */
    bool is_already_canal = HasTileWaterGround(tile - delta) && GetWaterClass(tile - delta) == WATER_CLASS_CANAL;

    WaterClass wc_lower = HasTileWaterGround(tile - delta) ? GetWaterClass(tile - delta) : WATER_CLASS_CANAL;
    Owner oc_lower = is_already_canal ? GetCanalOwner(tile - delta) : _current_company;
    bool add_cost_lower = !IsWaterTile(tile - delta);

    /* At this point we got a tile - delta with no bridge over it. Check for ownership. */
    if (IsWaterTile(tile - delta) && IsCanal(tile - delta)) {
        if (oc_lower != OWNER_NONE) {
            ret = CheckTileOwnership(tile - delta);
            if (ret.Failed() && !_settings_game.construction.build_on_competitor_canal) return ret;
        }
    } else {
        ret = DoCommand(tile - delta, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
        if (ret.Failed()) return ret;
        if (add_cost_lower) {
            cost.AddCost(ret);
            if (wc_lower == WATER_CLASS_CANAL) {
                if (oc_lower != OWNER_NONE) {
                    ret = CheckOwnership(oc_lower, tile - delta);
                    if (ret.Failed()) {
                        if (!_settings_game.construction.build_on_competitor_canal) return ret;
                    } else {
                        if (!is_already_canal) cost.AddCost(_price[PR_BUILD_CANAL]);
                    }
                }
            }
        }
    }