The company was fined £5,000 and ordered to pay costs of £1,851 to Environment Agency Wales who brought the prosecution.
The court was told that on July 8, 2002, Agency officers went to Amroth after receiving a complaint that sewage was discharging from manholes located at the rear of the Pirate Cafe and entering the Colby stream.
Investigations established that a valve being in the wrong position at the nearby Amroth sewage pumping station caused the problem. As sewage backed up the system. it discharged from manholes.
Subsequent investigations established that there had been problems with the sewers on July 6 and 7, which had not been adequately addressed.
Amroth is a Blue Flag bathing beach and recognised as such under European legislation.
Speaking after the case, an Agency spokesman said: "This incident clearly highlights the need to ensure that appropriate measures are taken to prevent pollution. The Agency will take enforcement action where management failures cause pollution of controlled waters. The seriousness of this incident and its potential impact on an EC designated bathing water has been reflected in the fine and costs."