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Stream Water Quality Trends in New Castle County, Delaware (1999-2014)

The University of Delaware defined water quality trends from 1999 to 2014 along 14 streams in New Castle County, Delaware.  Water quality improved or was constant at 94% of stations since 1999.  Dissolved oxygen, enterococcus bacteria, total nitrogen, total phosphorus, and total suspended sediment improved or were constant at 100%, 93%, 93%, 100%, and 86% of the water quality monitoring stations, respectively, since 1999.  During 2005–2010, median levels were good or fair at 100% of the stations for dissolved oxygen, 50% for bacteria, 71% for nitrogen, 86% for phosphorus, and 79% for sediment.  Since 1999, improving New Castle County water quality stations (43) outnumbered degrading stations (4) by a 10:1 margin.  Over the last decade and a half, watershed strategies such as the New Castle County National Pollution Discharge Elimination System (NPDES) Municipal Separate Stormwater System (MS4) Permit Program required by the Federal Clean Water Act have improved or preserved water quality along these streams, however, greater emphasis is needed to curb recent increases in nitrogen levels.