Pollution that that has killed tens of thousands of fish in a southern Minnesota creek is spreading slowly downstream toward the Minnesota River. The Minnesota Pollution Control Agency is investigating to see if a pipe leak reported September 14th by a vegetable processor in Montgomery is the main cause of the fish kill. Minnesota Public Radio's Mary Losure reports. Around 15 miles of Sand Creek-- a tributary that flows north to the Minnesota River--are now contaminated. What DNR officials describe as a "black slug" water has moved downstream from Montgomery and is now a few m