July 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 Reservoir0.9
2Tobacco River-0.7
3Kootenai Ft. Steele to Libby Dam3.3
4Kootenai River below Libby Dam2.7
5Fisher River0
6Yaak River1.4
7North Fk. Flathead River2.1
8Middle Fk. Flathead River1.9
9South Fk. Flathead River2.8
10Flathead River at Columbia Falls1.6
12Swan River2.1
13Flathead River at Polson1.9
14Mission Valley2
15Little Bitterroot River1.6
16Clark Fork River above Milltown1.6
17Blackfoot River2.3
18Clark Fork River above Missoula1.7
19Bitterroot River2.6
20Clark Fork River below Bitterroot River2
21Clark Fork River below Flathead River1.9
22Beaverhead River0.9
23Ruby River-0.2
24Big Hole River2.3
25Boulder River (Jefferson)0.2
26Jefferson River1.2
27Madison River1.2
28Gallatin River-0.2
29Missouri River above Canyon Ferry1
30Missouri River below Canyon Ferry0.5
31Smith River-2.3
32Sun River1.2
33Teton River-0.6
34Birch/Dupuyer Creeks1
35Marias River below Tiber Reservoir1.9
36Musselshell River1
37Missouri River above Fort Peck0.6
38Missouri River below Fort Peck 
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston3
42Shields River1.5
43Boulder River (Yellowstone)2.4
44Stillwater River3
45Rock/Red Lodge Creeks1
46Clarks Fork River3.5
47Yellowstone River above Bighorn River2.8
48Bighorn River below Bighorn Lake4
49Little Bighorn River1.6
50Yellowstone River below Bighorn River3.3
51Tongue River2.8
52Powder River2.4
53Upper Judith Basin-2.4
54St. Mary River0.9