Indicator: Chesapeake Bay Total Maximum Daily Load (TMDL) (1995-2023)

<p><strong>Access the Indicator Materials:</strong><br />- <a target='_blank' href='https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/chart-assets/AM-2023-TMDL-2025-06-17.pdf' rel='nofollow ugc noopener noreferrer'>Analysis &amp; Methods</a><br />- <a target='_blank' href='https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/Data-2023-TMDL-2025-06-17.xlsx' rel='nofollow ugc noopener noreferrer'>Data File</a></p><p>The Total Maximum Daily Load (TMDL) Indicator combines monitored and modeled data to estimate progress toward reductions in annual nitrogen and phosphorus loading rates in response to management practices, wastewater changes, population growth, land use change, and other factors. River discharge and nutrient concentrations are measured directly at River Input Monitoring (RIM) sites, while wastewater loads are estimated from EPA discharge monitoring adjusted by delivery factors in the Phase 6 Watershed Model. Nitrogen atmospheric deposition to tidal waters is also estimated using CMAQ-based dry and wet deposition models, and edge-of-tidal loads for the RIM and below-RIM watersheds are obtained from the Phase 6 Watershed Model.</p><p>The indicator uses the static Chesapeake Assessment Scenario Tool (CAST) to estimate long-term loads from a given watershed state, while the Dynamic Watershed Model accounts for lags in nutrient application and delivery to estimate current loads.</p><p><strong>Note: This Indicator supported progress tracking toward the Water Quality Standards Attainment and Monitoring Outcome in the original Chesapeake Bay Watershed Agreement, adopted in 2014. The Watershed Agreement and Clean Water Goal outcomes were revised in 2025.</strong></p>