October 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 Reservoir-1.4
2Tobacco River-0.9
3Kootenai Ft. Steele to Libby Dam-3.1
4Kootenai River below Libby Dam-1.8
5Fisher River-1.7
6Yaak River-1.9
7North Fk. Flathead River-2.6
8Middle Fk. Flathead River-3.1
9South Fk. Flathead River0.4
10Flathead River at Columbia Falls-0.2
12Swan River-1.2
13Flathead River at Polson-3.3
14Mission Valley 
15Little Bitterroot River 
16Clark Fork River above Milltown-0.9
17Blackfoot River-1
18Clark Fork River above Missoula-1.2
19Bitterroot River-0.7
20Clark Fork River below Bitterroot River-1.1
21Clark Fork River below Flathead River-2.5
22Beaverhead River0.2
23Ruby River-0.2
24Big Hole River-0.2
25Boulder River (Jefferson)-1
26Jefferson River0.2
27Madison River0.9
28Gallatin River-1.4
29Missouri River above Canyon Ferry-0.5
30Missouri River below Canyon Ferry-1.2
31Smith River-1.9
32Sun River-2.8
33Teton River-0.4
34Birch/Dupuyer Creeks-0.9
35Marias River below Tiber Reservoir0.2
36Musselshell River0
37Missouri River above Fort Peck-1.1
38Missouri River below Fort Peck 
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston1
42Shields River-1
43Boulder River (Yellowstone)-0.5
44Stillwater River0.5
45Rock/Red Lodge Creeks3
46Clarks Fork River2.6
47Yellowstone River above Bighorn River1
48Bighorn River below Bighorn Lake3.6
49Little Bighorn River-1.4
50Yellowstone River below Bighorn River2.2
51Tongue River-0.4
52Powder River-1.7
53Upper Judith Basin-3.2
54St. Mary River-2.8