1991 in Athens he won the 1500 m freestyle in 15: 14.30 min. Bronze behind his compatriot Jörg Hoffmann (gold in 15: 02.57 min.) And the Briton Ian Wilson (silver in 15: 03.72 min.) .
Things went even better for him in 1993 in Sheffield . The old and new European champion Jörg Hoffmann (gold in 15: 13.31 min.) Did not come close to the times of Athens, but Wieses time of 15: 14.76 min. Was enough to win the silver medal ahead of the Slovenian Igor Majcen (Bronze in 15: 15.05 min.).
In 1992 he reached the finals and came in 6th place in 3: 49.06 minutes, ahead of Stefan Pfeiffer , the second German finalist (gold was won by Russian Jewgeni Sadowy in the world record time of 3: 45.00 minutes).
In 1996 he only qualified for the B final, where he finished 2nd in 3: 52.37 minutes (10th place overall). In the A-final this time would have meant 8th place.