Registered Feature Sources

Introduction

The NLDI organizes indexed information into feature sources, each representing a dataset linked to the NHDPlusV2 hydrologic network. Discover feature sources programmatically and explore them through the NLDI API.

Feature sources may represent various hydrologic or environmental datasets, such as:

• Streamgages
• Water quality sampling locations
• Watershed outlets

Each feature within a source is accessed using a unique {featureID}.

Discovering Feature Sources

List feature sources by requesting the root endpoint with ?f=json:

https://api.water.usgs.gov/nldi/linked-data?f=json

The response is a JSON array of objects, each with source, sourceName, and features (a URL to that source’s feature collection).

Using a feature source, all items within that source can be retrieved via the feature listing endpoint. Requesting a feature source with no filters returns all features in that collection, which can be large. The endpoint supports limit and offset query parameters for pagination:

/linked-data/{featureSource}?limit=100&offset=0

See the Swagger UI for the complete parameter reference.

See also Client Libraries for Python and R examples of feature source queries.

Feature IDs

Every record in a feature source collection is assigned a {featureID}.
These IDs identify real-world hydrologic features such as monitoring stations,
observation wells, or catchment outlets.
They can be inspected directly:

/linked-data/{featureSource}/{featureID}?f=json

Special Feature Source: comid

The comid feature source corresponds directly to NHDPlusV2 catchment polygons
and their associated flowlines.
It exposes two useful capabilities:

• Direct access to catchment and flowline features
• A position endpoint that returns the catchment containing a given lon/lat
  using a point‑in‑polygon lookup

The comid source forms the backbone of NLDI navigation and indexing. The Fabric pygeoapi service provides detailed NHDPlusV2 geometry for flowlines, catchments, and waterbodies queryable by comid.

Catchment Indexing and Hydrographic Addressing

A key concept in understanding feature sources is the difference between:

1. Catchment indexing — assigning a feature to the NHDPlus catchment
   polygon that physically contains it.
   The NLDI uses this broadly, and the computation requires only a point-in-polygon test.

2. Hydrographic addressing — assigning precise hydrologic network
   locations using reachcode + measure pairs (“street name + house number”).
   These identifiers enable more accurate routing along hydrographic networks.

Some feature sources carry hydrographic addresses, depending on the dataset and the indexing method applied before data reach the NLDI.

Querying by Point

The comid feature source exposes a position endpoint that accepts a longitude/latitude coordinate in WKT format and returns the NHDPlusV2 catchment containing that point:

/linked-data/comid/position?f=json&coords=POINT(-89.35 43.0864)

This is useful for finding the catchment (and therefore the comid) for an arbitrary location before navigating the network.

Current Feature Sources (4/2026)

The following feature sources are registered in the NLDI as of early 2026. Discover the current list at any time with /linked-data?f=json.