May 2018
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 Reservoir2
2Tobacco River2.29999995231628
3Kootenai Ft. Steele to Libby Dam2.79999995231628
4Kootenai River below Libby Dam3.29999995231628
5Fisher River1.60000002384186
6Yaak River1.79999995231628
7North Fk. Flathead River2.5
8Middle Fk. Flathead River2.29999995231628
9South Fk. Flathead River2.5
10Flathead River at Columbia Falls2.5
12Swan River3.5
13Flathead River at Polson3
14Mission Valley 
15Little Bitterroot River 
16Clark Fork River above Milltown2.5
17Blackfoot River3.29999995231628
18Clark Fork River above Missoula3
19Bitterroot River2
20Clark Fork River below Bitterroot River2.70000004768372
21Clark Fork River below Flathead River2.90000009536743
22Beaverhead River1.10000002384186
23Ruby River1.10000002384186
24Big Hole River1.5
25Boulder River (Jefferson)2.79999995231628
26Jefferson River1.89999997615814
27Madison River1.60000002384186
28Gallatin River2.09999990463257
29Missouri River above Canyon Ferry2.09999990463257
30Missouri River below Canyon Ferry0.899999976158142
31Smith River2.70000004768372
32Sun River2.79999995231628
33Teton River2.09999990463257
34Birch/Dupuyer Creeks1.29999995231628
35Marias River below Tiber Reservoir2.79999995231628
36Musselshell River2.29999995231628
37Missouri River above Fort Peck1.10000002384186
38Missouri River below Fort Peck2.59999990463257
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston3.20000004768372
42Shields River3.59999990463257
43Boulder River (Yellowstone)2.59999990463257
44Stillwater River3.20000004768372
45Rock/Red Lodge Creeks0.100000001490116
46Clarks Fork River4
47Yellowstone River above Bighorn River3.29999995231628
48Bighorn River below Bighorn Lake2.29999995231628
49Little Bighorn River 
50Yellowstone River below Bighorn River2.29999995231628
51Tongue River-0.899999976158142
52Powder River1.10000002384186
53Upper Judith Basin 
54St. Mary River2.29999995231628