It's been six months since a suspected dumping of a toxic chemical wiped out 7800 trout in one of Minnesota's most popular trout streams. Authorities still don't know who is responsible. Even as the investigation continues, there are indications the stream is healing itself and will soon replenish the trout lost last August. Minnesota Public Radio's Mike Edgerly reports Hay Creek is one of the most studied, accessible and productive of southeast Minnesota's trout streams: The creek is a spring fed series of shallow rif