Sources and methods
Context Built from a Clean Water Hub snapshot of 2026-10-27, with public land-cover and weather data.
| Source | What it provides |
|---|---|
| Clean Water Hub (Izaak Walton League) | Every Save Our Streams survey: biological, chemical, Virginia SOS, Salt Watch, Nitrate Watch |
| USGS NLDI | The NHDPlus stream segment each site sits on |
| EPA StreamCat | Watershed land cover (NLCD 2019), soils, elevation, 1981–2010 climate, road crossings, population |
| Open-Meteo archive | Daily rainfall and air temperature for the week before each survey |
| Google Maps (links only) | Every map dot and site name opens the spot in Google Maps; no map tiles are loaded here |
Personal details (emails, phone numbers, names) are removed when the data is downloaded and never appear here.
Trends use the seasonal Kendall test, which compares a survey only with surveys from the same season in other years, with Sen slopes and at least 10 same-season comparisons. Turning points use a permutation test. Species groups are matched across the SOS and Virginia forms by a shared list of groups and pollution tolerance.
The expected-score model is gradient-boosted trees validated with five folds grouped by site, so each expected value comes from a model that never saw that site.
Code, tests and the full method notes: github.com/shankardba/iwla-river.