Northern pike
Toston Dam is threatened with environmental degradation due to invasive species. In 2009, the Montana Department of Fish, Wildlife and Parks (FWP) warned that the reservoir had been invaded by northern pike which had escaped from private ponds upstream. Northern pike are an aggressive predatory fish which feed on trout and other species highly prized by fishermen. A year later, the state sought approval to remove the limit on daily catches of northern pike to protect several trout species, which had come under severe pressure from the pike. In April 2011, the pike problem became so severe that the FWP announced an even more aggressive plan to try to remove the predatory fish from Toston Reservoir and other upstream waters.