Water quality trends from 1970 through 2005 were detected using the Seasonal Kendall test along 30 streams in the State of Delaware. Twenty-four streams flow east to the Delaware Bay and 6 streams flow west towards the Chesapeake Bay.
- Water quality improved or was constant at 69% of stations since 1990 and at 80% of stations since 1970-1980.
- Dissolved oxygen improved or was constant at 22 of 30 streams since 1990 and 8 of 25 streams since 1970-1980.
- Total suspended sediment improved or was constant at 21 of 28 streams since 1990 and 11 of 11 streams since 1970-1980.
- Enterococcus bacteria improved or was constant at 24 of 30 streams since 1990 and 25 of 27 streams since 1970-1980.
- Total Kjeldahl nitrogen improved or was constant at 14 of 29 streams since 1990 and 24 of 24 streams since 1970-1980.
- Total phosphorus improved or was constant at 19 of 29 streams since 1990 and 23 of 27 streams since 1970-1980.
- Median 2001–2005 levels were fair to good at 100% of DO stations, 75% for TSS, 48% for bacteria, 60% for TKN, and 43% for phosphorus.
- Water quality improves with increased forest area in Delaware watersheds.
Since the Federal Clean Water Act Amendments of the 1970s, improving water quality stations (50) outnumbered degrading stations (23) along Delaware streams by a 2:1 margin. Since 1990, degrading water quality stations (46) exceeded improving water quality stations (38) indicating a slight reversal from the early gains achieved since the implementation of the 1970s Clean Water Act amendments.
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