A sequence of events contributed to the health of the Chesapeake Bay in 2011, resulting in the second lowest Bay health score since assessments began in 1986. Increased levels of nitrogen and phosphorus washed into the bay during the wet spring, which led to decreased light levels and negatively affected aquatic grasses. During the summer, the hot, dry weather stimulated chlorophyll a in fresher surface waters, and low dissolved oxygen in saltier bottom waters. On August 27th, winds from Hurricane Irene mixed Bay waters, increasing dissolved oxygen. On September 7th rain from Tropical Storm Lee brought tons of sediment and fresh water to the mainstream, setting up conditions similar to the hot, dry summer.
