Fishing at Big Rock Detention Reservoir, Valley County, Montana

• Overview

  Big Rock Detention Reservoir lies within the bounds of Valley County, Montana. It sits at 2,260 feet above sea level. Ground here is low by Montana standards. Glasgow lies 17 miles from the water. The nearest city of size is Billings, 175 miles away. No border sits close enough to matter. It sits away from the main road, which keeps the noise down.

• Where to Fish on Big Rock Detention Reservoir

  Open data we checked carries no depth for this water. Levels move with the draw rather than the rain on water like this. Held water runs deepest at the wall and shallows back to the inflow. Species logged across Valley County include Chinook salmon, northern pike, cisco, walleye and yellow perch. Protected fish appear in the records for this area, so treat the list as information, not an invitation. Big Rock Detention Reservoir responds to conditions more than to tactics.

• Seasonal Patterns

  Average temperature peaks around 71°F in July and bottoms out near 13°F in January. A full turn of seasons, with the strongest sport on either side of summer. Winter fishing happens on the ice here, with open water back around early April. Expect the water usable from around early April until roughly late November. The open run goes from the thaw to the freeze, and April through October covers most of it. Anyone fishing Big Rock Detention Reservoir regularly works to that calendar.

• Tackle & Baits

  Nothing on record says whether the bank is open or closed. Public mapping marks it as seasonal water rather than permanent. Nothing built is recorded close to the bank here. Largemouth respond to soft plastics tight to cover; go weedless where the growth is heavy. A landowner's word beats anything printed elsewhere. Night access is frequently treated as a separate matter. The nearest alternative is Jordan Reservoir, 2.7 miles out. Treat access at Big Rock Detention Reservoir as something to verify.