This data release provides total nitrogen (TN) and total phosphorus (TP) annual loads for sites within the Chesapeake Bay, as well as ancillary data that describe potential nutrient sources and processes. The purpose of the study for which these data were developed is to test causal hypotheses, using structural equation models, related to the drivers of TN and TP load in the Chesapeake Bay over the period 1985-2012. The metadata document the sources of the original data and how the estimates were derived, including estimation of missing values.