Aquatic ecosystems are home to a complex intersection of physical and biological factors and an intersection of natural and anthropogenic factors. In the Chesapeake Bay, low oxygen events have occurred periodically and may be connected with harmful algal blooms, fish kills, heavy flooding/runoff events, and warming temperatures. Careful monitoring of the system by the Chesapeake Bay Program since 1984 allows scientists and policymakers to evaluate the causes of the events and monitor improvements in the health of the ecosystem.