The Iowa Department of Natural Resources says a fishkill in northern Linn County which was discovered over the weekend may have been caused by contaminated rainwater. A few hundred small fish, mostly minnows and chubs, were found dead Saturday along the east branch of the Blue Creek, a tributary of the Cedar River, near Walker. Investigators say high ammonia levels were found which may have come from a nearby feed mill and agricultural supplier on the south side of the town. A D-N-R spokesman says rainwater, pumped from a pit at the facililty, may have been contaminate, then carried by a stormsewer into the stream. The Cedar River will -not- likely be effected.