Great Seneca Creek

The Rockville Chapter's two monitoring sites on Great Seneca Creek in Germantown, Maryland, surveyed since 2005: how stream health has moved, which animals are changing and how the creek compares with what its setting predicts.

Compared with what its setting predictsSite 1 finds fewer pollution-sensitive animals than its setting predicts, and the gap appears to be widening (p = 0.055, about 11 percentage points a decade). Watch The score has held steadyScores held near 16.5 before 2013 and 16.6 since; the overall score shows no trend. Steady The mix of animals is shiftingBetween 2005–2009 and 2020–2024, damselflies and common net-spinning caddisflies became rarer while dobsonflies and aquatic worms became regulars. Watch Trend testsAt Site 1 the share of pollution-sensitive groups is declining (p = 0.042) while the total score shows no clear trend. Concern What moves the scorePollution-sensitive animals drive the swings: they add 2 to 18 points per survey. Context Season mattersSpring surveys average 2.6 points more than summer ones, so trends must compare like seasons. Context The chapter changed survey forms in 2024Since 2024 the chapter has also used the Virginia form, which the Hub's own site page does not chart. Context