The "hoot-owl" closure on the Sun covers from Highway 287 Bridge to the mouth of Muddy Creek west of Great Falls.
FWP's drought policy provides for angling closures when flows drop below critical levels for fish, when water quality is diminished, or when maximum daily water temperatures reach at least 73 degrees for three consecutive days.
The preferred water temperature for rainbow and brown trout is about 55-57 degrees. Temperatures of 77 degrees or more can be lethal to trout.
FWP officials said one of the best short-term strategies to address heat-induced stress in Montana's wild and native trout is to reduce catch-and-release mortality by alerting anglers to fish only in the morning.
"Fishing only in the cool morning hours can help," said Jason Mullen, FWP Region 4 fisheries biologist. "We're trying to minimize additional stress on wild trout during this summer of high water temperatures and low flows. This is really important among catch-and-release anglers who should reel in their catch and release it as fast as possible. Reducing the time on the line can really help the survival of trout this time of year."