Recognize that the legacy USGS NWIS /gwlevels service is fully decommissioned and migrate to the field-measurements OGC API

Steps

1. Do not build new integrations against https://waterservices.usgs.gov/nwis/gwlevels/ - its decommission schedule is already past: data was frozen Nov 1 2025, requests got 301 redirects to a USGS explainer blog post from Feb 1 2026 through Jun 1 2026, and since Jun 1 2026 requests return errors instead of data or redirects.
2. Replace any /gwlevels calls with the OGC API collection at https://api.waterdata.usgs.gov/ogcapi/v0/collections/field-measurements/items, filtered by monitoring_location_id.
3. Consult the field-by-field migration guide at https://api.waterdata.usgs.gov/docs/ogcapi/migration (section "Migrating from /gwlevels to /field-measurements") to map old WaterServices JSON fields onto the new response shape.
4. If existing client code still targets /gwlevels, expect outright request failures now (no data and no usable redirect), not the temporary redirect behavior USGS ran between Feb and Jun 2026.
5. For a free API key and rate-limit guidance on the replacement endpoint, see https://api.waterdata.usgs.gov/signup/.