OS Open Rivers
What it is
OS Open Rivers is Ordnance Survey's open dataset of the connected watercourse network of Great Britain — rivers, streams, canals, and the links between them — published under the Open Government Licence as part of OS OpenData. It is the go-to open layer for answering "is there a watercourse on or near this site?"
How it's produced
Derived and generalised from Ordnance Survey's detailed mapping into a connected network model. It is a cartographic/topological network product, not a hydrological survey — it tells you where watercourses are and how they connect, not their ecological condition or flow.
Update frequency & currency
Refreshed on OS's periodic OpenData release cycle. Good positional currency for the network; check the OS release date for the edition in use.
Spatial resolution / precision
Good positional accuracy for a national open product. The critical technical subtlety is geometry type: OS Open Rivers contains mixed geometry — narrow watercourses are represented as lines (LineString) while wide ones are polygons. Any spatial processing must handle both in a single layer.
Because the layer mixes lines and polygons, it must be loaded and queried as a generic geometry type, and area cannot be taken directly from a linear feature. For linear watercourses, a footprint has to be derived (e.g. by buffering) before any area-based calculation — computing area straight off a LineString yields zero and silently corrupts downstream scoring. This is a known handling requirement in the WildStack pipeline.
Known limitations
- Network, not condition. It shows presence and connectivity, nothing about water quality or ecological status — that is the WFD dataset's job.
- Generalised geometry. Suitable for presence/proximity, not for precise bank delineation.
- Mixed geometry types must be handled explicitly (see above).
How it compares to WFD Waterbody Classifications
They are complementary halves of "the water picture":
| OS Open Rivers | WFD Classifications | |
|---|---|---|
| Answers | Where is the watercourse? | What condition is the waterbody in? |
| Publisher | Ordnance Survey | Environment Agency |
| Nature | Network geometry | Ecological/chemical status per waterbody |
| Use together | Presence + proximity | Attach status to the reach |
Use OS Open Rivers to establish presence, then WFD to describe the reach's assessed status.
Role in BNG assessment
In WildStack's stack, OS Open Rivers drives the watercourse-present signal and provides watercourse geometry in the dataset hierarchy (sitting above the general land-cover layer for the specific question of watercourse features). Because rivers are handled as linear/mixed features, their area contribution is derived carefully rather than read off the geometry directly.
OS Open Rivers is a reliable, unglamorous workhorse — and the place where naive spatial code quietly breaks. The mixed line/polygon geometry catches people out: buffer a line to get an area and forget that some features are already polygons, and you either double-count or zero-out. We treat "is the geometry a line or a polygon?" as a first-class question for this dataset, not an afterthought. On the ecology side, remember its limit: it tells you a watercourse is there, never whether it's healthy. Pair it with WFD before you say anything about condition.
Official source
Last reviewed
5 July 2026. Revisit on a new OS OpenData release or any change to the product's geometry model.