Published
Once your pond counts as a dam, the state runs the calendar
Where this page starts
Idaho draws a line, and a pond on the far side of it stops being just a pond: it becomes a dam with a state program behind it. The threshold itself — and the separate question of whether the impounded water needs a water right — is covered on its own page. This page picks up the morning after: the pond counts, and now the state has requirements. They are concrete, they run in order, and most of them are quotable.
The scale of the program first: “IDWR currently regulates nearly 600 water storage dams and more than 20 mine tailings impoundment structures located throughout the state.” Your impoundment would be in that count.
An engineer draws it — twice
The state does not read owner-drawn sketches. Persons proposing a qualifying dam “must engage the services of a qualified professional engineer who is currently licensed in Idaho” — and the design documents bear that engineer’s seal and signature. Then the paperwork doubles:
“…shall submit duplicate plans, drawings and specifications of the proposed work to the director, and construction of a new dam or enlargement, or alteration or repairs shall not be commenced until the owner has applied for and obtained written approval of the plans, drawings and specifications.”
— Idaho Code §42-1712, construction of dams. Retrieved 28 September 2026
Two copies, one to keep — and one sentence that decides your calendar: no construction until written approval. Not “filed,” not “submitted” — approved. The statute lists what the plans carry:
- The owner’s name and address; the dam’s location, type, size, and height; the reservoir’s storage capacity.
- Subsoil and foundation conditions, site geology and hazards, and construction-material investigations, as the director requires.
Sixty days, fourteen days
“Plans, drawings and specifications submitted to the director complete with fees shall be approved or disapproved in no more than sixty (60) days and in no less than fourteen (14) days after receipt.”
— Idaho Code §42-1712. Retrieved 28 September 2026
A complete submittal with fees starts a clock: at least 14 days, at most 60. The floor matters as much as the ceiling — nobody gets same-week approval, so the dam belongs in the project schedule before the excavator does. Defective plans made in a good-faith attempt are not simply rejected; the director sends notice of defect and the owner has 30 days to perfect them.
Inspected while you build, then forever
The state follows the paper into the field. IDWR’s own page: “Inspection during construction shall be performed by IDWR for the purpose of securing conformity with the approved plans and specifications.” The rules add the owner’s duty to allow it, and a hold point:
“The owner shall allow inspections by the Department to assure the dam and appurtenant structures are constructed in conformance with the approved plans and specifications… The Department may request of the owner that certain stages of construction not proceed without inspection and approval by the Director.”
— IDAPA 37.03.06.035.07, Safety of Dams Rules. Retrieved 28 September 2026
After construction, the rhythm is statutory:
- “all dams or mine tailings impoundment structures regulated by the department shall be inspected at least once every five (5) years” (§42-1717).
- IDWR’s page repeats the same floor: “no less than every five (5) years” — with frequency tuned by condition, construction, age, hazard rating, and storage.
- Supervision of maintenance and operation “insofar as necessary to safeguard life and property” sits with the director of the Department of Water Resources.
Hazard class: what failure would do, not how big it is
The class that decides your obligations is assigned by consequences:
“Hazard classifications shall be assigned to new and existing dams based on the severity of failure consequences exclusive of the size or the physical condition of the dam.”
— IDAPA 37.03.06.025.02, Safety of Dams Rules. Retrieved 28 September 2026
A small dam above homes can out-class a big dam above grazing land. The high-hazard trigger is a measured one: IDWR “considers the inundation of residential structures with flood water from a dam break to a depth greater than or equal to two (2) feet to be a sufficient reason for assigning to a dam a high-hazard rating.” The rules’ table draws the band below it:
| Class | Flood water at habitation | Loss of life |
|---|---|---|
| Significant | potentially inundated at a depth of less than two (2) feet | unlikely to occur |
| High | potentially inundated at a depth of two (2) feet or greater | high probability |
What failure would do downstream is the whole question — not how new the dam is, how tall it is, or how it is maintained.
The Emergency Action Plan
Here the rule and the web page differ, and the rule controls:
“An Emergency Action Plan (EAP) is required for all Significant and High Hazard dams.”
— IDAPA 37.03.06.045, Safety of Dams Rules. Retrieved 28 September 2026
IDWR’s program page simplifies this to “a requirement for all owners of High hazard dams” — but the rule it enforces reaches Significant dams too. The timing is set as well:
“Before the initial filling of a reservoir, the owner shall file with the Director an EAP for review and approval.”
— IDAPA 37.03.06.045. Retrieved 28 September 2026
Not before the permit, not before winter — before the first fill. IDWR posts an “Idaho Dam Emergency Action Plan Fillable Form” on its forms page, so the format is not a puzzle to solve alone.
Numbers behind a default design
For new embankment dams, the rules publish default geometry an engineer works from:
- Upstream slope 3:1 or flatter — gentler on the water side.
- Downstream slope 2.5:1 or flatter.
- They are defaults, not ceilings: the rules say engineers should not consider them “a restriction to the use of other sound engineering design principles.”
For currency: the Safety of Dams Rules carry a text date of March 30, 2023, and IDWR’s program page was last updated September 17, 2026.
If the dam is found unsafe
The state’s enforcement is not a letter chain. Under §42-1717, an unsafe dam draws a written order to repair or remove — and if the owner neglects or refuses it, the director “may draw off all or part of such water” and keep it drawn off until the orders are complied with. Under §42-1718, where danger leaves no time for orders, the department may employ remedial means immediately — lower the water, empty the reservoir, take whatever steps are essential — and the bill lands on the owner:
“The cost and expenses of the remedial means provided in this act, including cost of any work done to render a dam, reservoir or mine tailings impoundment structure or its appurtenances safe, shall be recoverable by the state from the owner.”
— Idaho Code §42-1718, remedial means. Retrieved 28 September 2026
Unpaid 60 days after invoice, the director can sue in the district court where the dam sits.
The sequence, in order
- Engage an Idaho-licensed professional engineer before anything else moves.
- Submit duplicate plans with the application and fees — then wait out the 14-to-60-day decision.
- Build only after written approval, and let IDWR inspect during construction; expect hold points at certain stages.
- Learn your hazard class — assigned by failure consequences, with two feet of predicted inundation as the high-hazard line.
- File the EAP before the first fill if the class is Significant or High, using the state’s fillable form.
- Set expectations for the long run: an inspection at least every five years, and maintenance the state can order.
- Then the dirt: (208) 932-1140.
A dam-sized project never stands alone:
- The water in it is a water-right question.
- The ground it sits on passes through the county grading permit.
- The outlet that spills to a draw can meet the drainage standards that govern new construction.
- Land below it may sit in what FEMA’s flood maps show for Fremont County.
- Wet ground raises its own federal flag — filling near a marsh can need a Corps permit before any of the above.
Common questions
Who has to design a regulated dam in Idaho?
A qualified professional engineer currently licensed in Idaho. The design drawings, reports, and specifications must bear that engineer's professional seal and signature and go to IDWR for review and approval.
When can construction start on a regulated dam?
Only after written approval. Duplicate plans, drawings, and specifications go to the director with fees, and construction cannot commence until the owner has applied for and obtained written approval of them.
How long does IDWR have to approve or reject the plans?
A complete submittal with fees must be approved or disapproved in no more than 60 days and in no less than 14 days after receipt. Defective plans made in a good-faith attempt get a defect notice and 30 days to be perfected rather than an outright rejection.
Does IDWR inspect during construction?
Yes - inspection during construction is performed by IDWR to secure conformity with the approved plans and specifications, the owner must allow it, and the Department can hold certain stages of construction until they are inspected and approved.
How often is an existing dam inspected?
Every dam regulated by the department is inspected at least once every five years - the same floor IDWR's program page states as 'no less than every five (5) years.' Frequency can be higher depending on condition, construction, age, hazard rating, and storage.
What makes a dam High hazard?
Failure consequences, nothing else. IDWR treats inundation of residential structures from a dam break to a depth of two feet or greater as sufficient reason for a high-hazard rating; habitation inundated at less than two feet reads as Significant.
Does the hazard class depend on the dam's size or condition?
No - the rules assign hazard classifications based on the severity of failure consequences, exclusive of the size or the physical condition of the dam. A small dam over homes out-classes a large dam over undeveloped ground.
Who needs an Emergency Action Plan?
Under IDAPA 37.03.06.045, an EAP is required for all Significant and High Hazard dams. IDWR's web page simplifies this to High hazard owners, but the rule it enforces is broader - the rule controls.
When must the EAP be filed?
Before the initial filling of the reservoir, with the Director for review and approval. IDWR posts a fillable Idaho Dam Emergency Action Plan form on its forms page.
What are the default embankment slopes?
For new embankment dams the rules call for an upstream slope of 3:1 or flatter and a downstream slope of 2.5:1 or flatter - defaults an engineer may better with sound design, not ceilings.
What happens if IDWR finds my dam unsafe?
A written order to repair or remove; if the owner refuses, the director may draw off all or part of the water until the orders are complied with. In emergencies the department can act immediately - and the cost of any work done to render the dam safe is recoverable by the state from the owner, by district court suit if unpaid 60 days after invoice.