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Surface Water Supply Index

The Surface Water Supply Index (SWSI) is designed for areas that rely on snow melt as the primary source of surface water. The SWSI accounts for snowpack, mountain precipitation, streamflow, reservoir storage, and soil moisture conditions. The SWSI is used by irrigators, fisheries specialists, recreationalists, and others to evaluate current and seasonal surface water supplies.

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Find Historical Surface Water Supply Index Maps and Tables on the Montana Natural Resource Information System (NRIS) Web site