Beginning August 1 the Park closes The Madison River within the Park, the Gibbon River below Gibbon Falls and the Firehole River below Kepler Cascades to fishing. Water temps on each are approaching 80 deg. F. Look for these streams to be re-opened to fishing when water temps cool to more hospitable levels for trout. High water temperatures on other streams could result in more fishing limitations within the Park.
Consider that the higher one goes in elevation the less likely water temperatures will reach dangerously high levels for trout. Within the Park the waters at highest elevation are in the Yellowstone River drainage above the Upper and Lower falls, the Lewis River drainage above the canyon, the Fall River drainage from Beula Lake and above, and Bechler River in the upper canyon. All of these are over 7000 feet in elevation. Including these with the Gibbon River drainage above Gibbon Falls and the Firehole River above Kepler Cascades makes for plenty of water for concentrating fishing efforts with less impact on trout survival.