April 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 Reservoir0.899999976158142
2Tobacco River1.5
3Kootenai Ft. Steele to Libby Dam2
4Kootenai River below Libby Dam1.70000004768372
5Fisher River1.29999995231628
6Yaak River0.600000023841858
7North Fk. Flathead River2
8Middle Fk. Flathead River2.09999990463257
9South Fk. Flathead River3
10Flathead River at Columbia Falls2.29999995231628
12Swan River2.79999995231628
13Flathead River at Polson2.5
14Mission Valley4
15Little Bitterroot River 
16Clark Fork River above Milltown2.79999995231628
17Blackfoot River3.29999995231628
18Clark Fork River above Missoula3.20000004768372
19Bitterroot River1.79999995231628
20Clark Fork River below Bitterroot River2.70000004768372
21Clark Fork River below Flathead River2.59999990463257
22Beaverhead River1.10000002384186
23Ruby River1.5
24Big Hole River1.5
25Boulder River (Jefferson)2.79999995231628
26Jefferson River1.89999997615814
27Madison River1.29999995231628
28Gallatin River1.5
29Missouri River above Canyon Ferry1.79999995231628
30Missouri River below Canyon Ferry0.899999976158142
31Smith River2.70000004768372
32Sun River2
33Teton River1.20000004768372
34Birch/Dupuyer Creeks0.600000023841858
35Marias River below Tiber Reservoir2.5
36Musselshell River1.60000002384186
37Missouri River above Fort Peck0.699999988079071
38Missouri River below Fort Peck1.79999995231628
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston3.20000004768372
42Shields River3.40000009536743
43Boulder River (Yellowstone)2.59999990463257
44Stillwater River3
45Rock/Red Lodge Creeks-0.100000001490116
46Clarks Fork River3.70000004768372
47Yellowstone River above Bighorn River3.20000004768372
48Bighorn River below Bighorn Lake2.70000004768372
49Little Bighorn River 
50Yellowstone River below Bighorn River2.59999990463257
51Tongue River-0.600000023841858
52Powder River1.5
53Upper Judith Basin 
54St. Mary River2