Know your data sources.

Louisiana DEQ water-quality datasets. AGOL Feature Services, no auth. - search303dImpairedWaters ⭐ — IR2020 subsegments where a designated use is Not Supported (303(d)) - searchSubsegmentsByUse ⭐ — same layer, any use-rating - searchWatershedBasins (12), searchAmbientMonitoringSites (~761 LEAU active), searchFishAdvisories (62) - getServiceInfo quirks: subsegments + flowlines have NO parish — use BASIN (12 names: ATCHAFALAYA / CALCASIEU / ...) or bbox. Use codes: PCR/SCR/FWP/DWS/ONR/OYS/AGR/LAL. Status: Fully Supported / Not Supported / Insufficient Data / Not a Use / No Data Collected. Fish Advisories' Parishes is free-text ("Calcasieu and Cameron"); LIKE-matched. Air emissions + hazardous waste are NOT published as LDEQ Feature Services.

Mississippi Department of Environmental Quality MUSTER (UST + CERCLA) and 2024 Impaired Waters via opcgis.deq.state.ms.us. 5 curated layers covering petroleum tank sites, brownfield/CERCLA sites, 303(d) impaired waters, and completed TMDLs. - searchUSTSites ⭐ 11.9K active+inactive UST facilities - searchCERCLASites ⭐ 2.28K state CERCLA / brownfields with NPL flags - searchImpairedWaters ⭐ 233 streams + 4 polygons on the 2024 303(d) list - searchTmdlCompleted, getServiceInfo §0 caught: MUSTER does NOT support offset paging — handler iterates by OBJECTID. 5 scale-tier duplicate UST layers — only layer 10 exposed. BASIN column mixes UPPER and Title Case. POLLUTANT has numeric-prefix duplicates. Host has been historically flaky — handler retries once on 5xx/HTML.