The Minnesota Department of Natural Resources is investigating the deaths of hundreds of fish on the St. Croix River, which have been seen floating belly-up. However, DNR officials are claiming that this is a natural occurrence, as many of the fish are Gizzard Shad, a species which tend to die off around this time of year.

However, St. Croix River fishermen are claiming the dead fish is disconcerting, claiming to have also noticed multiple species including walleyes, crappies and sunfish floating dead.

The DNR are investigating the nearby power pant, Xcel Energy’s Allen S. King Power Plant, which was recently included among the 50 organizations fined for pollution by the Minnesota Pollution Control Agency. There may be a link to the plant going off line for a month and whether that had any effects on the St. Croix river.