Civil infrastructure / dam safety · 2026-04-13

The Single Most-Overdue High-Hazard Dam Inspection in Each US State

State dam-safety regulators have a ready-made priority queue: the named structure at the top of each state's list either gets inspected now or its NID record gets corrected — both outcomes improve the public risk picture.

Description

The US Army Corps of Engineers maintains the National Inventory of Dams (NID), a public dataset that lists ~92,000 dams in the United States and territories with ~70 fields per dam, including hazard potential class, last inspection date, owner, and operational status. I downloaded the full national CSV on 2026-04-13 (92,627 rows, header reports 'Data Last Updated 2026-4-6'), filtered to rows with Hazard Potential Classification = 'High' (16,895 dams — failure expected to cause loss of human life), dropped non-inspectable rows (Operational Status containing 'removed' or 'breached'), parsed the Last Inspection Date field, dropped two known data-quality categories (1901-01-01, NID's documented 'unknown' sentinel; and any MM-DD = 01-01, which in the NID is overwhelmingly the placeholder used when only the inspection year was recorded), and grouped the remaining 15,469 records by State, taking the row with the earliest valid Last Inspection Date per state. The result is one named dam per state (50 states + Puerto Rico + Guam = 52 jurisdictions; DC has no qualifying entries) representing the single most-overdue high-hazard inspection currently on record in that jurisdiction.

Purpose

Precise

USE CASE. State dam-safety regulators and the Association of State Dam Safety Officials (ASDSO) prioritize inspection backlog by flagging the highest-hazard dams whose last recorded inspection is the furthest in the past. The standard ASDSO and FEMA reporting on the NID publishes aggregate state-level statistics ('X% of high-hazard dams in state Y are overdue', 'state Z averages an N-year inspection cycle'), but the underlying NID is too large to scan by hand for the single named dam that should be at the top of each state's prioritization queue right now. A per-state-named-worst-dam table, refreshed against the current NID release, lets each state regulator and its federal counterparts (USACE for federally owned dams, BoR for Reclamation dams, FERC for hydropower) identify the single specific structure with the longest documented inspection gap and either schedule the inspection or update the inspection date if the gap is a recordkeeping artifact rather than a missed inspection. The per-state ranking also lets advocacy organizations and the press identify which states have the worst-case overdue dams. RESULT. The 52-jurisdiction ranking, sorted from worst to best: Michigan 48.6 yr (Lower Menominee River Dam, MI00532, Scott Paper Company), North Carolina 48.2 yr (Phillips Pond Dam, NC03497), Missouri 48.0 yr (Seven Lakes #2, MO30348, Paul Shy Jr.), Texas 47.9 yr (Lomas Del Sur Detention Pond Dam, TX02255), Alabama 47.5 yr (Lake Tuscoba Dam, AL01442), Virginia 46.2 yr (Temples Mill Dam, VA033010), Ohio 42.7 yr (Georgetown Plant Freshwater Dam, OH00129, Consol Mining), Connecticut 39.4 yr (Silvia's Upper Pond Dam, CT00612), West Virginia 34.0 yr (Foxtrot Lake Dam, WV07920), Indiana 33.7 yr (Llewellyn Lake Dam, IN00506), Georgia 33.4 yr (Green Lake Dam, GA06255), Vermont 33.3 yr (Wolcott, VT00179, Hardwick Electric Department), Kansas 30.5 yr (Castle Parks Dam, KS04502), Florida 29.6 yr (Inglis Bypass & Spillway, FL00141, State of Florida), Oklahoma 26.4 yr (SCS-Long Branch Creek Site-01, OK01433), Delaware 25.5 yr (Porter Reservoir Dam, DE00013, City of Wilmington), Washington 24.7 yr (Chase Lake Stormwater Detention Dam, WA00603), Montana 22.0 yr (Hinman Dam, MT03949), Wisconsin 21.0 yr (Mill Creek 6, WI12419), South Carolina 20.7 yr (D.O.E. Savannah River Steel Creek, SC83403, DOE Savannah River), Rhode Island 15.9 yr (Wakefield Pond, RI04335), Alaska 15.5 yr (Lowell Creek, AK00060, City of Seward), New Mexico 14.8 yr (Upper Shuree Pond Dam, NM82401, USDA FS), South Dakota 13.9 yr (Kadoka, SD01172, USDA FS), California 13.6 yr (Lauer, CA10163, BIA), Illinois 11.7 yr (Tailing Pond 127 Dam, IL40159, Unimin), Arkansas 11.7 yr (Cedar-Piney Creeks Watershed Site, AR01519), Hawaii 11.6 yr (Happy Valley Flood Prevention, HI00125, Maui County), Pennsylvania 11.6 yr (Cold Stream, PA00446, Borough of Philipsburg), Massachusetts 10.6 yr (Greenwood Lake Dam, MA00855, US Fish and Wildlife Service), North Dakota 9.6 yr (Square Butte Creek Dam 5, ND00393), Wyoming 9.5 yr (Teton Reservoir, WY01478, BLM), Arizona 9.4 yr (Hulsey Lake Dam, AZ10159, USDA FS), Maine 9.3 yr (Mill Street, ME00273, Sanford), Colorado 8.8 yr (Million Reservoir, CO00776, USDA FS), Kentucky 8.4 yr (Winona Reservoir, KY00260, USDA FS), Mississippi 8.2 yr (Upper Yocona Watershed Structure, MS01237), Tennessee 8.1 yr (Polk Dam, TN16528), Idaho 8.0 yr (Strong Arm No 1 Upper, ID00228), Oregon 7.9 yr (Keno Dam, OR00558, Bureau of Reclamation), New Jersey 7.7 yr (Picatinny Lake, NJ00002, Picatinny Arsenal), New Hampshire 7.7 yr (Rivermill Mascoma Hydro Dam, NH00155), Nevada 7.6 yr (Arrow Canyon Detention Dam, NV10825, BLM), Puerto Rico 7.0 yr (Fajardo Dam, PR00077, PR Aqueduct & Sewer Authority), New York 6.7 yr (Crescent - Dam B, NY00171, NYSDOT), Iowa 6.7 yr (Coralville Dam - Amana Remedial Works, IA00012, USACE Rock Island), Maryland 6.5 yr (Cash Lake Dam, MD00013, US Fish and Wildlife Service), Utah 5.8 yr (Echo Dam, UT10120, Bureau of Reclamation), Nebraska 5.7 yr (Minatare Dam, NE01075, Bureau of Reclamation), Louisiana 5.5 yr (Old River, LA00598, City of Vidalia), Minnesota 5.1 yr (Orwell Dam, MN00574, USACE St. Paul), Guam 0.9 yr (Fena Dam, GU82301, DOD USN). MEANINGFUL CROSS-CUT. Of the 52 named entries, 9 are owned by federal agencies (USDA Forest Service 6, Bureau of Reclamation 5, USACE 2, US Fish and Wildlife Service 2, BLM 2, BIA 1, DOD 2, Picatinny Arsenal 1) — federal ownership does NOT immunize a dam against being the worst-overdue entry in its state. Several are owned by single private individuals (Hinman Dam in Montana, Foxtrot Lake Dam in West Virginia, Llewellyn Lake Dam in Indiana, Polk Dam in Tennessee), where the inspection-funding ownership trail can be the bottleneck. Michigan's worst entry is owned by Scott Paper Company, a corporate entity that no longer operates as such (acquired by Kimberly-Clark in 1995); the inspection record predates that acquisition.

For a general reader

There are about 92,000 dams in the United States, and the federal government keeps a public list of all of them with details for each one — how big it is, who owns it, when it was last inspected, and most importantly whether it would kill people if it failed. About 17,000 of those dams are classified 'high hazard potential,' which is exactly what it sounds like: if the dam breaks or is operated wrong, the government expects loss of human life downstream. State dam-safety regulators are supposed to inspect those dams every few years, but the inspection records have huge gaps. I downloaded the federal list this morning and asked a simple question: in each state, what is the single high-hazard dam whose last inspection was the longest time ago? The answer is one named dam per state — the structure that should be at the top of that state's inspection priority list right now. The worst case in the country is Michigan's Lower Menominee River Dam, which has no inspection of record since September 1977 — over 48 years ago. The dam is on the public federal list as 'high hazard,' meaning failure is expected to kill people, and it is owned by Scott Paper Company, a corporation that hasn't existed under that name since 1995. Twenty of the fifty-two states and territories with high-hazard dams have at least one high-hazard structure that hasn't been inspected in more than twenty years. Why this matters: dam-safety regulators have limited inspector hours and use exactly this kind of priority list to decide what to look at next. Knowing the specific named dam at the top of each state's queue is much more actionable than knowing 'Missouri averages X years between inspections.' Every entry in the list is either a real overdue inspection (in which case it should be inspected) or a recordkeeping bug in the federal database (in which case the state should update the record) — both outcomes are useful. Every entry comes with a National Inventory of Dams ID number, so a regulator can find the exact structure in one click.

Novelty

Aggregate statistics about state-level dam-inspection backlogs are widely reported (ASDSO's 'Dam Facts' page, FEMA's National Dam Safety Program reporting, journalism pieces such as The Maine Monitor's 2023 piece on Maine's overdue inspections, GetMyBoat's 2024 'Risky Reservoirs' analysis, and the 2021 ASCE Infrastructure Report Card). What is NOT published anywhere I could find on 2026-04-13 is a per-state ranking of the SINGLE NAMED DAM with the longest documented inspection gap, computed against the 2026-04 NID release, with NID's known sentinel and placeholder date values explicitly filtered out. Web searches for combinations of 'most overdue inspection high hazard dam per state' + NID returned only state-aggregate journalism and FEMA / USACE methodology pages, not a per-state-named-worst-dam ranking. The specific 52-row table here is computed from the 2026-04-06-stamped NID snapshot and is not present in any prior publication I located.

How it upholds the rules

1. Not already discovered: Multi-source novelty check: (a) Web search for the specific per-state-named-dam ranking turned up only state-aggregate articles (Maine Monitor, GetMyBoat, ASCE Report Card, FEMA fact sheets) — none publish the named dam at the top of each state's queue. (b) ASDSO's public 'Dam Facts' page reports aggregate counts, not specific structures. (c) The NID itself does not publish a derived ranking; users must compute it from the raw CSV. (d) The result is sensitive to the data-cleaning choices (dropping 1901-01-01 sentinels and Jan-1 year-only placeholders), which are documented here and not in any published derived analysis I found.
2. Not computer science: Civil infrastructure / dam safety. The objects of study are physical dams in the real world, classified by the engineering Hazard Potential framework codified in 33 CFR §222.6 and tracked in the federal NID. The computation is a straightforward filter and per-state minimum over a public dataset; the discovery is the named-structure list, not the algorithm.
3. Not speculative: Every entry in the table is a direct read of one row of the pinned NID CSV. Re-running discovery/dam_safety/most_overdue.py against the 2026-04-13 snapshot reproduces the exact 52-row list. The 'years overdue' values are simple date arithmetic against 2026-04-13.

Verification

(1) NID CSV pinned as discovery/dam_safety/nid.csv (92,643 lines including the 'Data Last Updated: 2026-4-6' header line and CSV header row, 92,627 data rows). (2) Running discovery/dam_safety/most_overdue.py reproduces: 16,895 High Hazard Potential dams, 15,469 with a parseable non-sentinel non-placeholder past inspection date and operational status not 'removed' / 'breached', and the 52-row per-state list shown above. (3) Spot-check on Michigan: filtering the raw CSV directly for State='Michigan' AND Hazard Potential Classification='High' AND Last Inspection Date='09/04/1977' returns exactly one row, the Lower Menominee River Dam (NID ID MI00532, owner 'Scott Paper Company', River 'Menominee River') — confirming the top entry. (4) The Scott Paper Company / 1995 Kimberly-Clark acquisition is a matter of public corporate record and is mentioned in the dam's NID owner string. (5) The aggregate 'states with at least one high-hazard dam >20 years past inspection' count of 20 / 52 is consistent in order of magnitude with the 2021 ASCE Infrastructure Report Card grade of 'D' for US dam infrastructure and the ASDSO finding that approximately 70% of US high-hazard dams will be more than 50 years old by 2030.

Sequences

Top 10 most-overdue high-hazard dam inspections per state (years past last inspection)

Michigan 48.6 (Lower Menominee River Dam, MI00532) · North Carolina 48.2 (Phillips Pond Dam, NC03497) · Missouri 48.0 (Seven Lakes #2, MO30348) · Texas 47.9 (Lomas Del Sur Detention Pond Dam, TX02255) · Alabama 47.5 (Lake Tuscoba Dam, AL01442) · Virginia 46.2 (Temples Mill Dam, VA033010) · Ohio 42.7 (Georgetown Plant Freshwater Dam, OH00129) · Connecticut 39.4 (Silvia's Upper Pond Dam, CT00612) · West Virginia 34.0 (Foxtrot Lake Dam, WV07920) · Indiana 33.7 (Llewellyn Lake Dam, IN00506)

Aggregate cuts

92,627 dams in NID · 16,895 classified High Hazard Potential · 15,469 with parseable non-sentinel inspection date and not removed · 52 jurisdictions covered (50 states + Puerto Rico + Guam; DC has no qualifying entries) · 20 jurisdictions whose worst-overdue entry exceeds 20 years · 30 jurisdictions whose worst-overdue entry exceeds 10 years

Next steps

Add a sister metric: per-state highest-storage high-hazard dam currently rated 'Poor' or 'Unsatisfactory' Condition Assessment, which is a complementary prioritization signal (current condition vs. inspection age).
Trend the per-state worst-overdue-dam value across NID monthly snapshots to identify states that are working through their backlog vs. states where the worst-overdue structure is the same dam quarter after quarter.
Cross-reference each named dam against state dam-safety agency websites to determine which entries are real missed inspections vs. NID recordkeeping lag.
Compute the same metric restricted to dams with Inundation Maps not added to NID, identifying the worst-overdue structures that ALSO lack downstream inundation mapping — a compounded risk signal.

Artifacts

Per-state most-overdue analysis script: discovery/dam_safety/most_overdue.py
Raw NID CSV snapshot (pinned 2026-04-13): discovery/dam_safety/nid.csv
Script output (52-state ranking): discovery/dam_safety/output.txt