Driving by part of Montana’s Big Hole River recently, I commented to my girlfriend that it was surprising not to see anyone out fishing in what looked like great trout water.  Being no stranger to Montana, she noted that the state’s Department of Fish, Wildlife and Parks closes many rivers when the water temperatures get too high.  Such closures are a new concept to me, so I decided to check it out.

Just this month, several of Montana’s major trout fishing destinations were closed by the FWP due to warming water temperatures.  According to protocol, whenever one of the major trout rivers in the state reaches or exceeds 73 degrees F for three straight days, closures are imposed.  Most of the rivers are closed from 2 pm to midnight, but some 24 hour closures exist.

The reasoning behind the fishing closures is that as the water warms and begins to approach their upper critical threshold for survival, trout become increasingly more stressed.  Add to this the stress of being caught by anglers, and fishing mortality becomes much higher.  When a fish is caught and released, it needs access to cool, oxygenated water to fully recover.  Warmer water holds less oxygen, and therefore makes it harder for captured fish to survive the ordeal.

The closures oftentimes last the entire summer, depending on stream temperature.  See a list of recent fishing closures in Montana here.