Fluctuation in water flow, and consequently high water temperatures, is the key reason the fishing drops off and this can be attributed to a variety of reasons . . . The gauging station is located between Melrose and Glen, and when planning a float trip down the Big Hole it is a good idea to call first . . . Records show that the average flow of the Big Hole over a 64 year period was 1,162 cfs. To put the minimum flow figure in perspective, when the Big Hole was closed to fishing for a few months starting in August of 1994, the flow was measured at the Melrose gauge around 130 cfs. Winters in the Big Hole Valley can be quite severe.
Temperatures are often brutal, dropping well below zero.
When the upper river begins to thaw in spring, good fishing is not far off. In fact, you can fish much of the river whenever there is open water. During early spring the water level on the 'Hole' will normally be low. Not like summertime lows, but low nonetheless. March will see a slight rise in the river, but it isn't until April and May that there is a significant increase in volume due to snow melt.