State fisheries officials remain puzzled as to the cause of hundreds of dead carp found floating in Holter Reservoir over the last month.
Most of the carp died around the Fourth of July with only a few additional mortalities observed after the holiday weekend.
When the fish were first discovered, tissue samples were collected and sent to a lab. But even with the disease testing results the cause of the deaths remains a mystery, though several possible causes were ruled out.
It does not appear to be caused by an infectious bacteria or virus and has apparently not affected any other fish species in the reservoir, which lies between Great Falls and Helena.
The die off is likely a combination of factors such as old age, diet, water quality and parasites.
In the meantime, FWP will continue to monitor fish populations and water quality to try to determine what may have caused the carp die off.