April 2017
Surface Water Supply Index Report

Provided by the US Natural Resources Conservation Service
Bozeman, Montana

The SWSI is designed for areas that rely primarily on snowmelt runoff as the primary source of surface water. The SWSI accounts for snowpack, mountain precipitation, streamflow, reservoir contents, and soil moisture conditions. The SWSI can be used by irrigators, fisheries personnel, recreationists, and others who utilize surface waters. SWSI values are categorized as follows:

IDBasin NameSWSI
1Marias River above Tiber Reservoir0.52
2Tobacco River1.39
3Kootenai Ft. Steele to Libby Dam2.95
4Kootenai River below Libby Dam3.62
5Fisher River0.87
6Yaak River1.39
7North Fk. Flathead River2.08
8Middle Fk. Flathead River1.39
9South Fk. Flathead River3.47
10Flathead River at Columbia Falls2.95
12Swan River1.39
13Flathead River at Polson2.26
14Mission Valley1.62
15Little Bitterroot River-0.7
16Clark Fork River above Milltown0.69
17Blackfoot River0.17
18Clark Fork River above Missoula0.52
19Bitterroot River0.35
20Clark Fork River below Bitterroot River0.469
21Clark Fork River below Flathead River1.61524
22Beaverhead River0.17
23Ruby River-1.39
24Big Hole River0
25Boulder River (Jefferson)-1.22
26Jefferson River0.42
27Madison River0.35
28Gallatin River-0.69
29Missouri River above Canyon Ferry-0.17
30Missouri River below Canyon Ferry0
31Smith River-0.76
32Sun River0.87
33Teton River0.95
34Birch/Dupuyer Creeks-0.69
35Marias River below Tiber Reservoir2.43
36Musselshell River-0.87
37Missouri River above Fort Peck1.2915
38Missouri River below Fort Peck1.04
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston3.13
42Shields River-1.04
43Boulder River (Yellowstone)0
44Stillwater River1.74
45Rock/Red Lodge Creeks-0.52
46Clarks Fork River3.47
47Yellowstone River above Bighorn River2.527
48Bighorn River below Bighorn Lake3.18535
49Little Bighorn River0
50Yellowstone River below Bighorn River3.18535
51Tongue River1.56
52Powder River1.04
53Upper Judith Basin0.2
54St. Mary River1.74