This research focused on developing and evaluating nitrogen-stable isotope condition assessment bioindicators and monitoring methods for low gradient coastal stream systems to assist states in assessing the condition of low-gradient coastal systems. Low-gradient coastal stream systems support important landscape level ecological functions by connecting uplands and marshes directly to large tidal rivers, estuaries, and coastal waterbodies. In this study we develop and evaluate innovative monitoring and assessment methods to support biological indicator development for waterbody types and taxa that lack nationally consistent and reliable approaches. Low-gradient tidal and non-tidal coastal stream systems are infrequently included in national and regional monitoring programs and may require different methods than freshwater streams (US EPA National River and Streams Assessment) or large tidal rivers (US EPA National Coastal Condition Assessment). Results from this study demonstrate that stable isotopes of nitrogen (δ15N) bioindicators from a variety of biotic trophic levels can be used as an efficient and effective rapid monitoring tool for assessing biotic condition in low gradient coastal systems. These stable isotope indicators also provide empirical field measurements for ground-truthing national indices which are derived from remotely sensed national landscape data layers. The δ15N biotic responses were consistently significant across all trophic levels and negatively correlated with landscape level stressor exposure conditions reflected in the national and regional scale indices. Verifying national multiscale indices with site-scale field measured bioindicators (δ15N) provides coastal managers, states, tribal, regional, and local watershed organizations confidence in using these national indices at local watershed and catchment scales for identifying and prioritizing protection for healthy coastal stream networks and watersheds, as well as targeting critical functional elements of watersheds for restoration efforts. This dataset is associated with the following publication: Kuhn, A., M. Schwartz, J. Serbst, J. Lake, L. Coiro, and M. Charpentier. Ground truthing national multiscale landscape indices with nitrogen-stable isotopes for low-gradient coastal stream ecosystems. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, USA, 198: 339, (2026).