Great Seneca Creek Record
About

About this record

An independent analysis of the Izaak Walton League's Save Our Streams data, built to follow how a stream's ecology changes over time. It starts with the Rockville Chapter's sites on Great Seneca Creek in Germantown, Maryland, and reads them against every volunteer sample in the country.

How volunteers sample

Save Our Streams volunteers work in riffles, the fast, shallow, stony stretches of a stream. They stir the stones upstream of a net, then sort and count the animals that wash in. Insects such as mayflies and stoneflies only live in clean water, so the mix of animals found says how healthy the stream is. Other volunteers test water for chloride from road salt and for nitrate with test-strip kits.

not to scaleRiffle: fast, shallow water over stoneswhere Save Our Streams samplesPool: slower and deeperKick-seine netstir the stones upstream; animals wash inMost animals counted cling toand under the stones
Illustration. Animals in the lens are drawn far larger than true.

How to use it

  1. Explore opens on a map of where samples are taken. Filter by sample type, colour the watershed rings by the measure you care about, and click a ring to zoom from a region down to a small subwatershed. Press / to search.
  2. At the smallest watersheds, click a biological site to see its own history: every survey, what it found, and what was expected for its season and setting.
  3. Findings collects the results, each with the evidence and method behind it. Great Seneca Creek has the chapter's own story.

Sources and care

Survey data comes from the Izaak Walton League's Clean Water Hub (snapshot 2026-10-27). Watersheds are USGS hydrologic units; watershed land cover is from EPA StreamCat; rainfall from the Open-Meteo archive; state outlines from the US Census Bureau. See Sources and methods.

Personal details are never shown. Many salt and nitrate kits test home taps, so those sites carry no names and their locations are rounded to about 1 km. Volunteer data is valuable and noisy: every result here says how strong its evidence is.