June 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 Reservoir0.800000011920929
2Tobacco River0.400000005960464
3Kootenai Ft. Steele to Libby Dam2.59999990463257
4Kootenai River below Libby Dam3.79999995231628
5Fisher River0.300000011920929
6Yaak River-0.100000001490116
7North Fk. Flathead River0.600000023841858
8Middle Fk. Flathead River1.10000002384186
9South Fk. Flathead River3.20000004768372
10Flathead River at Columbia Falls1.5
12Swan River0.800000011920929
13Flathead River at Polson1.29999995231628
14Mission Valley 
15Little Bitterroot River 
16Clark Fork River above Milltown0.800000011920929
17Blackfoot River0.600000023841858
18Clark Fork River above Missoula0.100000001490116
19Bitterroot River1.10000002384186
20Clark Fork River below Bitterroot River0.400000005960464
21Clark Fork River below Flathead River1
22Beaverhead River1.60000002384186
23Ruby River0.899999976158142
24Big Hole River1.60000002384186
25Boulder River (Jefferson)3.20000004768372
26Jefferson River1.89999997615814
27Madison River1.29999995231628
28Gallatin River0.899999976158142
29Missouri River above Canyon Ferry1.10000002384186
30Missouri River below Canyon Ferry0.899999976158142
31Smith River2
32Sun River1.29999995231628
33Teton River1
34Birch/Dupuyer Creeks2.5
35Marias River below Tiber Reservoir2.59999990463257
36Musselshell River1.5
37Missouri River above Fort Peck1.79999995231628
38Missouri River below Fort Peck2.59999990463257
39Milk River 
40Dearborn River near Craig 
41Yellowstone River above Livingston2
42Shields River1.70000004768372
43Boulder River (Yellowstone)2.09999990463257
44Stillwater River2.5
45Rock/Red Lodge Creeks2.09999990463257
46Clarks Fork River3.20000004768372
47Yellowstone River above Bighorn River2.40000009536743
48Bighorn River below Bighorn Lake0.899999976158142
49Little Bighorn River-0.800000011920929
50Yellowstone River below Bighorn River0.899999976158142
51Tongue River-0.400000005960464
52Powder River0.800000011920929
53Upper Judith Basin 
54St. Mary River1.5