design was never intended to serve as a warning for boaters. On this record, we are not “left with the definite and firm conviction that a mistake has been committed.” United States Gypsum Co., 333 U.S. at 395, 68 S.Ct. at 542. Moreover, the cases cited by appellants to support their failure to maintain argument are inapposite. These cases concern the government’s failure to maintain various navigational aids, such as buoys and lighthouses. The government’s decision to provide the service, ie., to place a buoy or erect a lighthouse, was held to be a discretionary decision, but the government’s failure to maintain thé structure was not within the discretionary function exception. See, e.g., Indian Towing Co. v. United States, 350 U.S. 61, 69-70, 76 S.Ct. 122, 126-27, 100 L.Ed. 48 (1955) (<HOLDING>); Denham v. United States, 834 F.2d 518, 520-21
holding that the discretionary function exception may apply in the absence of a conscious decision  holding that decision to operate lighthouse is discretionary decision while failure to maintain lighthouse is not within discretionary function exception holding that decision to operate a lighthouse service as an aid to navigation is an exercise of discretion recognizing a discretionary function exception to that waiver holding that the united states could be liable under the ftca for the negligent operation of a lighthouse despite the fact that the initial decision to undertake the lighthouse service was discretionary