Project goals of the Freshwater Ecoregional Measures for the Northern Great Plains Steppe (NGPS) were to: 1) identify and reevaluate the number, diversity and viability of aquatic target occurrences within the Montana portion of the NGPS Ecoregional Plan based on a suite of indicator-based measures set within the aquatic ecological system framework, and 2) determine biodiversity viability measures (for the aquatic ecological system types, or for target species), threat status, and protection of these targets within the portfolio sites of the Ecoregional Plan. This document reports on that work.