Complex sentence: Grass carp have been captured in every Great Lake except Lake Superior, but there is so far no evidence of a reproducing population, although a juvenile grass carp was caught in a river leading to Lake Scugog.
Split into simpler sentences: Grass carp have been captured in every Great Lake except Lake Superior. But there is so far no evidence of a reproducing population although a juvenile grass carp was caught in a river leading to Lake Scugog.