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St. Anthony’s own hazard rankings: the water comes first, and the floodplain changes shape outside the city line
The city’s own hazard ranking puts water first
Every comprehensive plan has a hazards chapter; most are boilerplate. St. Anthony’s 2023 plan is unusually specific, and its rankings come from the county’s All Hazards Mitigation Plan. The 2016 update of that plan assessed twenty-eight potential hazards — natural, biological and man-made — and its conclusion for this city is two words long:
“…reaches similar conclusions related to likelihood and severity of potential hazards with ‘River Flooding’ and ‘Dam Failure’ identified as the highest ‘overall hazard risk rating.’”
— City of St. Anthony 2023 Comprehensive Plan, hazards chapter, describing the 2016 Fremont County All Hazards Mitigation Plan. Retrieved 23 September 2026
The plan adds the local reason plainly: “St. Anthony’s position in relation to rivers makes it vulnerable to flood risk from each of the three upstream dams discussed in the plan, if they were to fail.” Around that sentence the chapter assembles its flood picture:
- Three upstream dams, each a flood-risk source for the city if it failed — named as three, none of them identified by name in the plan itself.
- Inundation maps exist — drawn in the All Hazards Mitigation Plan, showing significant flooding upstream and downstream of the city.
- Flash flooding and recreation hazards rank medium county-wide but “somewhat higher” for the St. Anthony area.
Where the floodplain actually sits — city versus belt
The plan’s flood paragraph carries a distinction a buyer should not skip, because the river runs straight through town:
“The floodplain is limited to areas directly adjacent to the Henry’s Fork river in St. Anthony but spreads out in lower lying areas in the Area of City Impact.”
— City of St. Anthony 2023 Comprehensive Plan, hazards chapter. Retrieved 23 September 2026
Inside the city, the mapped floodplain hugs the river. Outside the limits — in the belt — it spreads. Ground that reads as safely away from the river can sit in lower-lying floodplain once you cross the city line, which is one more reason the belt boundary question is worth answering in writing. Two records sit behind that map line:
- NFIP participation. The city is in the National Flood Insurance Program, which the plan summarizes in one sentence: it “requires that all buildings in the floodplain meet certain standards and obtain flood insurance.”
- Map 8. The FEMA-designated floodplain is drawn on the comprehensive plan’s own Map 8 — a page worth asking for at the city office.
Fire: the plan’s caution and the CWPP’s rating sit side by side
Two statements in the chapter pull in opposite directions, and both are true. First the caution, in the plan’s own words — drought years, irrigated farmland that stays green only while water lasts, and “a large fire in late summer could easily spread to dry farmland, grain fields, or even yards and homes, especially if wind conditions are favorable.” Then the formal rating, which quotes the Community Wildfire Protection Plan:
“This categorizes St. Anthony within the ‘Fuel Zone 1, Lower Valley,’ which is ‘generally not critically threatened by wildfire,’ and ‘classified as low severity with a mean fire interval of 0-35 years.’”
— City of St. Anthony 2023 Comprehensive Plan, hazards chapter, quoting the Community Wildfire Protection Plan. Retrieved 23 September 2026
“Mean fire interval of 0–35 years” is not a promise of 35 quiet years — it is the historical average stretch between burns in this fuel zone. The CWPP’s own recommendations are the practical takeaway for a house on the edge of farmland:
- Fire-resistant building materials on new construction.
- Vegetation management — the treated zone around structures.
- The plan’s own caution stands: in drought years, irrigated farmland stays green only while water lasts, and a late-summer fire could spread to dry farmland, grain fields, or yards and homes.
Earthquakes: high state ranking, quiet local record
The plan records that Idaho ranks fifth in the nation for earthquake risk, and assembles the local record:
- Significant quakes felt here — including the Borah Peak earthquake in Custer County and the 1959 Yellowstone earthquake.
- No major damage or injuries in St. Anthony from an earthquake since settlement, on the plan’s own account.
For what that means to a building, the city’s seismic design category is its own question, answered on the seismic category page: B, on Site Class B soil, per the USGS design service.
The policies behind the chapter
Four of the chapter’s adopted policies describe how the city intends to steer building away from the hazards above:
- Discourage building on hazardous ground — review and where necessary rewrite building and zoning regulations to discourage developing “potentially hazardous” land such as floodplain areas, and ensure seismic code standards are followed in new construction.
- Dual access for subdivisions — review subdivision ordinances to require two ways in and out of each new subdivision, for evacuation.
- Stay in the NFIP — and pursue actions that reduce flood damage to city property and infrastructure on the Henry’s Fork.
- A wildland-urban interface overlay — designate WUI areas as a special land use overlay.
The dual-access policy is the one that shows up in plat review — if you are splitting ground, expect the second access question. The county’s own application paperwork asks about canals and floodplain before anything else; those routing questions are mapped on their own page.
Before you buy ground on the strength of this
- Ask the city for Map 8 from the comprehensive plan — the FEMA-designated floodplain, on the city’s own map.
- If the parcel is outside the limits, remember the plan’s sentence: the floodplain spreads in lower-lying belt ground. Verify, don’t extrapolate.
- Ask at both desks for the All Hazards Mitigation Plan’s inundation maps — the dam-failure scenarios are drawn, not described.
- Edge-of-farmland lot? Read the CWPP recommendations as a materials list, not a footnote.
- Splitting ground? Bring up dual access before the plat does.
- Then call (208) 656-1745 and pressure-test what the maps said about your parcel.
Common questions
What is the biggest natural hazard in St. Anthony?
Water. The 2016 Fremont County All Hazards Mitigation Plan rated 'River Flooding' and 'Dam Failure' as the highest overall hazard risks, and the city's 2023 plan notes its position among rivers makes it vulnerable to flood risk from each of three upstream dams if they were to fail.
Where is the floodplain in St. Anthony?
Inside the city it is limited to areas directly adjacent to the Henry's Fork, per the 2023 comprehensive plan - but it spreads out in lower-lying areas of the Area of City Impact outside the limits. The FEMA-designated floodplain is drawn on the plan's Map 8.
Is St. Anthony in the National Flood Insurance Program?
Yes. The city participates, which the plan summarizes as requiring that all buildings in the floodplain meet certain standards and obtain flood insurance.
Is wildfire a serious risk in St. Anthony?
Formally, low: the Community Wildfire Protection Plan places the city in Fuel Zone 1, Lower Valley - 'generally not critically threatened by wildfire,' low severity, mean fire interval of 0-35 years. The plan still warns that in drought years fire could spread to dry farmland and homes, and recommends fire-resistant materials and vegetation management.
What does a 0-35 year mean fire interval mean?
It is the historical average time between fires in that fuel zone - a severity classification, not a schedule. A 'low severity' rating with that interval describes typical fire behavior in the zone, not a guarantee about any particular year.
Is St. Anthony at risk of earthquakes?
Idaho ranks fifth in the nation for earthquake risk and the area has felt significant quakes, including the Borah Peak earthquake and the 1959 Yellowstone earthquake, but the city records no major damage or injuries from one since settlement. New construction follows seismic code standards - the city's seismic design category is B.
What hazard-related rules affect new subdivisions?
The hazards chapter's policies include discouraging development on hazardous ground such as floodplain, and reviewing subdivision ordinances to require dual access into and out of each new subdivision for evacuation.
What hazard maps can I actually see for St. Anthony?
Three, from two desks: the comprehensive plan's Map 8, showing the FEMA-designated floodplain, held with the plan at the city office; the All Hazards Mitigation Plan's dam-failure inundation maps, held county-side; and the city's storm drainage map, also at the city office.