An isolated wetland is a wetland that does not abut a relatively permanent water of the United States. It can still be wet. It can still be a three-parameter wetland under the Corps manual. Isolated describes the connection, not the soil.
On the Gulf Coast that often looks like a depressional flatwoods wetland, a pitcher-plant bog, an interdunal swale, or a farmed wet pocket that does not touch a creek, bayou, or ditch that is itself a water of the United States.
Isolated is not the same as “not a wetland”
A delineation can map an isolated feature as wetland. The plants, soils, and hydrology can all be there. The jurisdictional question is whether that wetland has a continuous surface connection to a water that is already federal. If it does not, it is isolated for Clean Water Act purposes.
National Wetlands Inventory polygons do not answer this. NWI was not drawn to decide 404. Neither does a wet spot on aerials.
Why isolation matters after Sackett
Before Sackett v. EPA (2023), many of these features were pulled into 404 under a “significant nexus” theory — a hydrologic or ecological connection that was not a surface abutment. The Supreme Court rejected that test. The current federal test is narrower: a relatively permanent water, plus a continuous surface connection (abutting / touching). EPA and the Corps said so again in their March 2025 field memo.
So an isolated wetland may no longer need a Section 404 permit to fill. That is a federal answer. It is not a state answer.
State programs still apply
Mississippi, Alabama, Louisiana, and Florida did not repeal their wetland, 401, or coastal programs when Sackett came down. Florida’s ERP path is its own project even when the Corps is out. Alabama and Mississippi still run 401 and coastal consistency where those programs attach. Local floodplain and stormwater rules stack on all of that.
“Isolated” is a reason to ask for an approved JD. It is not a reason to mobilize a dozer.
How you actually tell
You still start with a delineation: where is the wetland line? Then you look at the connection — or the lack of one — to a relatively permanent water. That is a site fact: topography, ditches, culverts, berms, tide, and whether any surface connection is real or a line on a map.
A pipe or culvert does not automatically create a continuous surface connection under the 2025 field memo. Neither does a berm you can see over. Those are the facts the Corps is using right now. The agencies have a broader WOTUS rewrite in process; until that rule is final, this is the field test.
What we do with that
If the feature is isolated and the Corps agrees, the 404 piece may drop. The state piece, the floodplain piece, and the engineering piece may not. If the feature abuts a tidal creek or a relatively permanent tributary, it is not isolated, and you are back on the ordinary 404 path.
Cypress Environment & Infrastructure maps the line first, then tells you whether isolation is a real argument or wishful thinking. We work from Biloxi, Mobile, and Pensacola, in the Mobile, Vicksburg, Jacksonville and New Orleans Districts. Office hours are Monday–Friday, 9 a.m.–5 p.m.
See What is a jurisdictional determination? and Sackett v. EPA.