May 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 Reservoir0.69
2Tobacco River1.56
3Kootenai Ft. Steele to Libby Dam2.78
4Kootenai River below Libby Dam1.99
5Fisher River1.56
6Yaak River2.26
7North Fk. Flathead River2.43
8Middle Fk. Flathead River2.08
9South Fk. Flathead River3.99
10Flathead River at Columbia Falls3.65
12Swan River3.3
13Flathead River at Polson2.43
14Mission Valley2.31
15Little Bitterroot River2.9
16Clark Fork River above Milltown1.04
17Blackfoot River1.39
18Clark Fork River above Missoula1.39
19Bitterroot River0.87
20Clark Fork River below Bitterroot River1.234
21Clark Fork River below Flathead River1.99944
22Beaverhead River0.69
23Ruby River-0.17
24Big Hole River0.35
25Boulder River (Jefferson)-0.17
26Jefferson River0.83
27Madison River1.22
28Gallatin River0.17
29Missouri River above Canyon Ferry0.17
30Missouri River below Canyon Ferry0.52
31Smith River0.38
32Sun River0.69
33Teton River0.95
34Birch/Dupuyer Creeks-0.69
35Marias River below Tiber Reservoir2.6
36Musselshell River-0.17
37Missouri River above Fort Peck1.6105
38Missouri River below Fort Peck1.22
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston3.3
42Shields River1.88
43Boulder River (Yellowstone)1.04
44Stillwater River2.08
45Rock/Red Lodge Creeks0.35
46Clarks Fork River3.47
47Yellowstone River above Bighorn River2.785
48Bighorn River below Bighorn Lake3.99
49Little Bighorn River1.56
50Yellowstone River below Bighorn River3.32725
51Tongue River2.78
52Powder River2.95
53Upper Judith Basin-1.9
54St. Mary River2.08