By Kjel Jones, independent excavation & dirt-work researcher for Island Park · licensed Idaho real estate agent, LPT Realty

Published 2026-10-02

The free wetlands map answers the biology. The permit question needs the Corps

The free map, and its fine print

Marsh corners, wet meadows, lake margins — Island Park has all of them, and the first stop for any landowner wondering about one is free: the U.S. Fish & Wildlife Service’s National Wetlands Mapper. Type in a parcel and it draws every mapped wetland on it, with type and extent.

Then read the fine print before relying on it, because the Service writes the limit of its own map in plain words:

“The wetlands displayed on the Wetlands Mapper show wetland type and extent using a biological definition of wetlands. There is no attempt to define the limits of proprietary jurisdiction of any federal, state, or local government, or to establish the geographical scope of the regulatory programs of government agencies.”

— U.S. Fish & Wildlife Service, National Wetlands Inventory, Wetlands Mapper. Retrieved 28 September 2026

In other words: the mapper answers whether the ground is wet in the biological sense — not whether a wetland is regulated The same page repeats it as a caution: NWI data “should not be interpreted as representing the presence, absence, or extent of wetlands that may be covered under one or more federal, state, Tribal, or local laws.” A blank map is not a green light, and a green map is not a permit denial.

The permit law the map does not apply

The federal law at issue is Section 404 of the Clean Water Act: discharging dredged or fill material into waters of the United States is a permitted activity, and the permit comes from the U.S. Army Corps of Engineers. Digging a pond in a wet meadow, filling a low spot, pushing a driveway pad across a swale — those can all be discharges of fill. The mapper cannot tell you whether your spot counts; the Corps can, and the Service’s own recommendation for planned work near wetlands is to contact the local USACE regulatory office before you commit a machine to the ground.

What Congress exempted

The statute carves ongoing rural work out of the permit requirement. Three of the exemptions, verbatim:

“(A) from normal farming, silviculture, and ranching activities such as plowing, seeding, cultivating, minor drainage, harvesting for the production of food, fiber, and forest products, or upland soil and water conservation practices;
(B) for the purpose of maintenance, including emergency reconstruction of recently damaged parts, of currently serviceable structures such as dikes, dams, levees… and transportation structures;
(C) for the purpose of construction or maintenance of farm or stock ponds or irrigation ditches, or the maintenance of drainage ditches;”

— Clean Water Act §404(f)(1)(A)-(C), 33 U.S.C. 1344(f). Retrieved 28 September 2026

Read the adjectives, because they carry the weight: normal farming, currently serviceable structures, farm or stock ponds. The exemptions protect continuing agriculture and upkeep of what already exists — not new construction. One boundary ties them all together, in plain English: a discharge whose purpose is to bring the wet area into a use it was not previously subject to, in a way that impairs flow or shrinks the reach of the water, needs a permit after all.

Nationwide Permit 18: the small-fill lane

When a permit is needed, most small fills do not need an individual one. Nationwide Permit 18 — Minor Discharges — covers them if every limit holds:

“(a) The quantity of discharged dredged or fill material and the volume of area excavated do not exceed 25 cubic yards below the plane of the ordinary high water mark or the high tide line; (b) The discharge of dredged or fill material will not cause the loss of more than 1/10-acre of waters of the United States; and (c) The discharge of dredged or fill material is not placed for the purpose of a stream diversion.”

— U.S. Army Corps of Engineers, Nationwide Permit 18, Minor Discharges, 2026 reissuance. Retrieved 28 September 2026

Twenty-five cubic yards is a block of material 3 feet deep over 225 square feet — and note that excavated volume counts toward the same limit, not just fill placed. A tenth of an acre is 4,356 square feet of loss. And a diversion of a stream is outside the lane entirely.

The notification catch

Here is the part that surprises people: NWP 18 is not self-service. The same permit text requires notice to the Corps before the work starts:

“The permittee must submit a pre-construction notification to the district engineer prior to commencing the activity if: (1) the discharge of dredged or fill material or the volume of area excavated exceeds 10 cubic yards below the plane of the ordinary high water mark or the high tide line, or (2) the discharge of dredged or fill material is in a special aquatic site, including wetlands.”

— Nationwide Permit 18, notification clause, 2026 reissuance. Retrieved 28 September 2026

Catch (2) is the one that matters in wet country: any discharge into a wetland triggers the notification, even a small one. In practice that means most Island Park fills near a marsh go through the district engineer, on paper, before the machine moves.

The 2026 clock

Nationwide permits are not permanent law; they come in sets with expiration dates, and the calendar just turned:

• The 2021 set expired March 14, 2026 — any article, PDF, or district page quoting it is quoting a dead permit.
• The Corps reissued the program on January 8, 2026 (Federal Register document 2026-00121, 91 FR 768).

“The 57 NWPs, the general conditions, and the associated definitions will go into effect on March 15, 2026. The NWPs will expire on March 15, 2031.”

— Federal Register, 2026-00121 (91 FR 768), published January 8, 2026. Retrieved 28 September 2026

Five years of runway — and a reason to date-check anything an older neighbor tells you about a nationwide permit.

Walk it through: one marshy corner, step by step

1. Map it. Pull the parcel up on the Wetlands Mapper and print or screenshot what it shows — wetland types, boundaries, and the disclaimer.
2. Walk it. Boots on the ground, in spring if you can. Mapped and actual wetlands do not always agree, and the mapper makes no legal claim either way.
3. Hold the fill outside the wet line if the project allows it — grading, staging, and stockpiles placed away from the wet area avoid the question entirely.
4. Size what cannot be avoided. Discharge and excavation together, in cubic yards, below the ordinary high water mark. Under 10 and outside a wetland, NWP 18 runs without prior notice; anything more, or anywhere in a wetland, means a pre-construction notification.
5. Notify the district engineer before work when the triggers hit — the notification, not the digging date, starts the clock.
6. Ask the Corps regulatory office for the jurisdictional answer when the stakes are real: they can tell you what the mapper cannot.
7. Sort the other desks at the same time — work in a live channel is a different permit entirely, and the county will ask about wetlands on its own grading application. Then bring the ground itself: (208) 932-1140.

The other desks a wet corner can pull in

A marshy parcel rarely sits at just one desk:

• Work in the channel of a continuously flowing stream takes an IDWR stream channel alteration permit, not a Corps permit.
• FEMA’s flood maps for Fremont County decide a different question — what the county requires inside a floodplain — and a blank online map there is missing data, not missing hazard.
• The county’s excavation and grading permit asks about wetlands on its own application.
• If the wet spot becomes a pond, the water-right and dam-threshold questions follow it.
• And if the plan is to mine the ground instead of fill it, gravel extraction runs a different county track entirely.

Common questions

How do I check whether my land has wetlands on it?

Start with the free FWS National Wetlands Mapper - it draws mapped wetlands by type and extent for any parcel. Walk the ground too, ideally in spring, because the map and the ground do not always agree.

Is the Wetlands Mapper a legal determination?

No. The mapper shows wetlands using a biological definition, and the Service states there is no attempt to define the limits of any government's jurisdiction or the scope of regulatory programs - and that NWI data should not be interpreted as showing the presence, absence, or extent of wetlands covered by law. Only the Corps can make the jurisdictional call.

Do I need a permit to dig or fill near a marsh?

If the work discharges dredged or fill material into waters of the United States, Section 404 of the Clean Water Act requires a Corps permit - though small fills may qualify under Nationwide Permit 18, and normal farming, ranching, and pond or ditch work are exempted by statute.

What does the farming and ranching exemption cover?

Discharges from normal farming, silviculture, and ranching activities - plowing, seeding, cultivating, minor drainage, harvesting - plus maintenance of currently serviceable structures like dikes and dams, and construction or maintenance of farm or stock ponds, irrigation ditches, and drainage ditches. The key adjectives are normal, currently serviceable, and farm or stock.

What is Nationwide Permit 18?

The small-fill lane of the Corps permit program, called Minor Discharges: up to 25 cubic yards of discharge and excavation below the ordinary high water mark, no more than 1/10-acre of loss, and no stream diversion. Meet every limit and a separate individual permit is not needed.

How big is 25 cubic yards, really?

It is the equivalent of 3 feet of fill over 225 square feet - a driveway apron, not a building pad - and the limit counts excavation volume together with fill placed, not fill alone.

When does NWP 18 require pre-construction notification?

Whenever the discharge or excavated volume exceeds 10 cubic yards below the ordinary high water mark, or the discharge is in a special aquatic site - which includes wetlands. That second trigger means nearly any wetland fill in Island Park country goes through the district engineer on paper first.

Are the current nationwide permits still valid?

The 2021 set expired March 14, 2026. The Corps reissued the program effective March 15, 2026: 57 NWPs running through March 15, 2031, under a final rule published January 8, 2026. Date-check anything older.

Who decides if my wet spot is federally regulated?

The Army Corps of Engineers, through its regulatory office - not the Fish and Wildlife Service and not the mapper. The Service itself recommends contacting the local USACE regulatory office before conducting activities that could affect waters or wetlands.

Does the county permit cover this instead?

No - the county's excavation and grading permit is separate and will ask about wetlands on its own application, but it is not a Section 404 permit. The two can apply to the same project at once.

What if a stream runs through the wet area?

That adds an Idaho desk: altering the channel of a continuously flowing stream takes an IDWR Stream Channel Alteration permit - joint application 60 days ahead, with its own timeline - on top of whatever the Corps requires.

Does building a pond in the wet spot need a water right?

If the pond impounds water, IDWR treats that as storage, and storage generally needs a water right - with a separate dam-safety threshold if the impoundment is large enough. That question is covered in its own page on this site.