The lack of standardized data collected has limited our ability to quantify aquatic resource conditions and determine stressors of degraded conditions across large scales. Additional challenges, particularly in dryland regions, have included high natural spatial and temporal variability of condition metrics and dispersed land uses that are poorly represented in national geospatial datasets. We conducted two large-scale probabilistic surveys of perennial streams on Bureau of Land Management (BLM) lands in the continental western U.S. from 2013-2015 and 2019-2022 to determine aquatic resource conditions, trends, and stressors. We assessed the condition of 13 biological, chemical, and physical habitat metrics. To account for natural spatial and temporal variability when determining conditions, we used recent models that use field and remote sensing datasets to predict site-specific reference conditions. We used relative risk and random forest modeling to assess stressor-response relationships and sources of stressors. Stressors and their associated sources were assessed both with field data and national and agency specific geospatial datasets. We were able to infer the conditions of a total of 18,423 and 17,324 perennial stream km on BLM from 2013-2015 and 2019-2022, respectively. Chemical (total nitrogen, total phosphorous, and salinity) and biological (macroinvertebrate assemblage composition) metrics had the greatest extent of poor conditions (26-37% of stream km). Reaches with excessive total nitrogen were twice as likely to have poor macroinvertebrate assemblage conditions from 2013-2015. For both total nitrogen and macroinvertebrate assemblages, the extent of stream km in poor condition decreased by 10% between survey one and two. However, salinity, percent fine sediment, percent shade, and temperature conditions posed high risks to macroinvertebrates in 2019-2022. Sources of excessive nutrients were primarily agriculture and livestock or wild horse and burro grazing. Sources of excessive salinity were primarily oil and gas wells and agriculture. Additionally, excess nutrient concentrations and salinity and poor macroinvertebrate conditions were associated with streams with a high likelihood of hydrologic alteration. These results will assist the BLM with prioritizing management actions and achieving their goal of sustaining the health, diversity, and productivity of public lands for the use and enjoyment of present and future generations