Review of the available data on water quality in Chesapeake Bay has revealed changes over recent decades caused by enrichment with nutrients. In the upper and middle bay, and several tributaries, concentrations of algae present during the summer months have increased since the mid 1960's. There have been decreases in the clarity of the water associated with increased algal stocks. Nutrient concentrations have also increased, phosphorus more notably so than nitrogen. In some of the tributaries increased algal production has led to reduced concentrations of oxygen below the halocline in the middle part of the estuary. Oxygen concentrations in the open bay have not changed greatly with the possible exception of extreme conditions, as during periods of extensive ice cover. Since 1969 or 1970, however, stocks of many anadromous species and marine spawners representing higher tropic levels have declined to new long-time lows.

"September 1982"