WallDockDeck
Marathon · Monroe County

How high does a seawall have to be in Marathon?

No minimumset in local code

Marathon's Land Development Regulations set no minimum or maximum seawall top elevation in any datum. The city fixes a two-foot cap width and a six-inch retention swale, berm or curb behind the wall, but the height comes from your engineer's design and your permits.

Source: City of Marathon Code, Appendix A Land Development Regulations, Sec. 106.36(H) Hardened Shorelines; also Secs. 106.38(F), 104.64(B)(16), 107.102.11(E)(1), 108.20(B) · Verified 2026-10

The detail

No fixed elevationMarathon LDR Sec. 106.36(H), Hardened Shorelines, sets the rules for bulkheads and seawalls and states no top elevation in NAVD88, NGVD29 or any other datum.
When a wall is allowedOnly on residential canals and altered shorelines, and only where riprap or sloping rock revetments with biotechnical erosion control will not suffice, as determined by the City Biologist. Sec. 106.36(H).
Replacement or severe erosionAllowed when replacing an existing deteriorated bulkhead or seawall, or to stabilize a severely eroded shoreline where riprap is shown not to be sufficient. Sec. 106.36(H)(1).
Cap widthSeawalls may have a cap of two feet in width. Sec. 106.36(H)(1).
Retention behind the wallThe design must include a minimum six-inch retention swale, berm or curb directly landward of the wall. Sec. 106.36(H)(5).
Wall lineThe bulkhead line is set at the property's average mean high water line when the permit is requested, and reclaiming eroded land by bulkheading and backfilling is prohibited. Sec. 106.36(H)(6).
No open waterNo new vertical seawalls or bulkheads on open water shorelines, and none on or waterward of a sea turtle nesting beach. Sec. 106.36(H)(3) and (H)(4).
Engineer requiredAll waterfront construction such as docks, piers, seawalls or revetments shall be planned and designed by a professional engineer. Sec. 104.64(B)(16).
V zonesIn coastal high hazard areas, bulkheads and seawalls need other-agency authorization, must stand clear of buildings, and need a design professional's analysis showing no harmful diversion of floodwaters or wave runup. Sec. 107.102.11(E)(1).

Your city's height sheet

The elevation your city requires, the datum it is measured in, and the section of code that says so. One page.

Available for the cities whose rule we have verified and sourced.

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The county rule behind this

What applies across Monroe County, and where each city departs from it.

Monroe CountySeawall requirements county-wide

The same question, nearby

The rule changes at the city line, not the county line.

MonroeKey WestMonroeIslamorada

Other questions about Marathon

Seawall permit processDo I need a permit to repair a seawall in Marathon?Dock permit & size limitsHow big a dock can I build in Marathon?Boat lift rulesWhat are the boat lift rules in Marathon?Waterfront deck requirementsWhat are the deck setback and railing rules in Marathon?Storm prep & documentationWhat are the storm and debris rules in Marathon?

Twelve signs a seawall is failing

What to look for, where to look for it, and what it means when you find it. Walk your wall in twenty minutes.

A screening sheet for owners, not an engineering inspection.

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