We expected that this section would have the best water quality of all three sections due to the "mouth washing" effect that happens twice a day with the tidal action of the cleaner Potomac River. However, this was not the case.
The % Score of DO in the Lower DC Anacostia was the worst among the 3 sections. Historically this section has occasionally been the worst, perhaps because all Combined Sewer Overflows (CSOs) occur in this section and the southernmost end of the Upper DC Anacostia, discharging an estimated 1.483 billion gallons of raw sewage every year into the river.
In this section, the % Score of Secchi Disk Depth was also very low. In all 3 sections water clarity (Secchi disk depth) has been degrading in recent years. Water clarity and submerged aquatic vegetation, which are interrelated, were the only reviewed parameters that show decline. Pollution from runoff is probably only slightly increasing in DC because the DC portion of the watershed is almost built-out. On the contrary, the suburban area in Maryland is the victim of sprawl, developing more acres of impervious surfaces that increase the volume and velocity of stormwater runoff. This increased volume has been generating much higher spikes of peak stream flows in streams that erode the streambanks and scour the streambed. Because small particles of sediment will not settle down easily, they contribute to degraded water clarity in the entire Anacostia River.
Click here to download a printable version of the 2011 State of the Anacostia River.