Buy a camp on a lake, and you inherit more than a view. You inherit a set of boundary lines, water rights, and access rules that most buyers never see coming. A plat of survey is the one document that sorts this out. It shows where your land actually ends, who may own the ground under the water, and whether that path to the dock is really yours to use.
Lakes, rivers, and coastal shorelines all come with their own rules. A plat of survey is where those rules get drawn out in black and white. Here is what to look for.
The Ordinary High-Water Mark: How a Plat of Survey Defines Where Your Land Ends
Water levels rise and fall all year. A pond looks different in April than it does in August. So a surveyor does not use the water’s edge on the day of the survey to set your property line.
Instead, the plat shows the ordinary high-water mark. This is the line based on the water body’s long-term, natural high-water pattern, not a single storm or a dry summer. It is the legal boundary between private land and the water below it.
This line matters more than most owners realize. It affects:
- Where you can legally build a dock or boathouse
- How much dry land you actually own near the shore
- Where erosion or fill has quietly shifted the usable yard over time
If your plat does not clearly mark this line, ask your surveyor to explain how it was set and what evidence was used.
Great Pond Law in Maine: Why the State May Own the Land Beneath Your Lake Frontage
Maine has an old rule that surprises a lot of new lakefront owners. Under colonial-era law dating back to the 1640s, natural water bodies over 10 acres are called Great Ponds. The land beneath a Great Pond is generally held in trust by the state, not owned by the person who owns the shore.
This rule protects public rights to fish, boat, and travel across the water, even on a lake that looks fully private from the road. It does not take away your ownership of the dry land or your frontage rights. But it does mean the state, not you, typically holds title to the submerged land offshore.
A plat of survey is where this shows up clearly. It should note the high-water line as the edge of private ownership, with the submerged land beyond it treated separately. If your plat is silent on this, it is worth asking your surveyor to confirm how the water body is classified.
Deeded vs. Prescriptive Access: Reading Right-of-Way Notations to the Water
Not every path to the water is created equal. A plat of survey usually draws a clear difference between two kinds of access.
Deeded access is a formal, recorded right-of-way. It is written into a deed, shown as a defined strip on the plat, and legally protected. Prescriptive access is different. It is a path that has been used openly for years, sometimes decades, without ever being formally granted.
A surveyor can locate and plot a well-worn trail. But locating a path is not the same as confirming a legal right to use it. If your plat shows an unlabeled trail to the shore, do not assume it is protected. Ask whether it is backed by a recorded easement or whether it may need legal confirmation.
Riparian and Littoral Boundaries: What the Plat Reveals About Your Water Rights
Water rights depend on what kind of water you border. Riparian rights apply to land along a river or stream. Littoral rights apply to land along a lake or the ocean.
The difference matters more than it sounds.
- On many rivers and streams, boundary lines can extend to the center, or thread, of the waterway.
- On lakes and irregular shorelines, surveyors often use a different method, drawing boundary lines out from the shore based on angles to the water, since a lake shore rarely runs in a straight line.
This affects dock placement, how far your rights extend into the water, and how shared frontage gets divided between neighboring lots. A plat that correctly labels your frontage as riparian or littoral gives you a much clearer picture of what you can and cannot do near the water.
Shared Docks, Access Corridors, and Easements on Neighboring Waterfront Lots
Older camp and cottage neighborhoods were often laid out with narrow shared strips of land leading down to the water. These corridors gave landlocked “back lots,” the ones set behind the shorefront row, a legal way to reach the lake.
Decades later, these narrow strips are a common source of tension. A plat of survey can show:
- The exact width and location of a shared access corridor
- Whether it is meant for foot traffic only or also for a shared dock
- How many properties actually hold rights to use it
If you own a back lot, or you border one, this is one of the most useful things a plat can confirm before a dispute starts.
Frequently Asked Questions
Does a plat of survey show who owns the land under a lake or river?
It can show the boundary line, but ownership of submerged land, especially under Maine’s Great Pond law, is often separate from ownership of the adjoining upland and may belong to the state.
What is the ordinary high-water mark, and why does it matter for my dock?
It is the legal reference line that separates private land from public trust water. It affects how far out a dock or structure can be built.
Can a plat of survey confirm my right to cross a neighbor’s land to reach the water?
A plat can show a recorded right-of-way or access easement. It cannot confirm an unrecorded or verbal arrangement. That requires deed research beyond the plat itself.
Are all lakes in Maine treated the same under Great Pond law?
No. The designation generally applies to natural water bodies over 10 acres, which changes public access and ownership rules compared to smaller private ponds.
What if I’ve used a path to the water for years, but it’s not shown on my plat?
Long-term, open use may support a prescriptive easement claim, but that is a legal determination separate from what the plat itself documents.
